diff --git a/.clang-tidy b/.clang-tidy
index c84ba323b604..af99026e5d70 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -54,7 +54,7 @@ Checks: >
 
 # In order to trigger an error, you must have a rule defined both in checks and in this section.
 WarningsAsErrors: >
-    cppcoreguidelines-no-malloc, performance-unnecessary-copy-initialization
+    cppcoreguidelines-no-malloc, modernize-use-nullptr, performance-unnecessary-copy-initialization
 
 # Todo: define a better regex match that includes most project headers, but excludes third party
 # code.
diff --git a/src/c_api/c_api_executor.cc b/src/c_api/c_api_executor.cc
index b99350525bfa..c3a64736c010 100644
--- a/src/c_api/c_api_executor.cc
+++ b/src/c_api/c_api_executor.cc
@@ -130,7 +130,7 @@ int MXExecutorBindX(SymbolHandle symbol_handle,
                           num_map_keys, map_keys, map_dev_types, map_dev_ids,
                           len, in_args, arg_grad_store, grad_req_type,
                           aux_states_len, aux_states,
-                          NULL, out);
+                          nullptr, out);
 }
 
 int MXExecutorBindEX(SymbolHandle symbol_handle,
diff --git a/src/io/iter_image_det_recordio.cc b/src/io/iter_image_det_recordio.cc
index b93370026616..62e362c17277 100644
--- a/src/io/iter_image_det_recordio.cc
+++ b/src/io/iter_image_det_recordio.cc
@@ -303,7 +303,7 @@ inline void ImageDetRecordIOParser<DType>::Init(
         dmlc::InputSplit::Blob blob;
         while (reader.NextRecord(&blob)) {
           rec.Load(blob.dptr, blob.size);
-          if (rec.label != NULL) {
+          if (rec.label != nullptr) {
             if (param_.label_width > 0) {
               CHECK_EQ(param_.label_width, rec.num_label)
                 << "rec file provide " << rec.num_label << "-dimensional label "
@@ -416,7 +416,7 @@ ParseNext(std::vector<InstVector<DType>> *out_vec) {
       std::vector<float> label_buf;
       if (this->label_map_ != nullptr) {
         label_buf = label_map_->FindCopy(rec.image_index());
-      } else if (rec.label != NULL) {
+      } else if (rec.label != nullptr) {
         if (param_.label_width > 0) {
           CHECK_EQ(param_.label_width, rec.num_label)
             << "rec file provide " << rec.num_label << "-dimensional label "
diff --git a/src/io/iter_image_recordio.cc b/src/io/iter_image_recordio.cc
index e8dcbef2e909..066cad973774 100644
--- a/src/io/iter_image_recordio.cc
+++ b/src/io/iter_image_recordio.cc
@@ -226,7 +226,7 @@ ParseNext(std::vector<InstVector<DType>> *out_vec) {
       mshadow::Tensor<cpu, 1> label = out.label().Back();
       if (label_map_ != nullptr) {
         mshadow::Copy(label, label_map_->Find(rec.image_index()));
-      } else if (rec.label != NULL) {
+      } else if (rec.label != nullptr) {
         CHECK_EQ(param_.label_width, rec.num_label)
           << "rec file provide " << rec.num_label << "-dimensional label "
              "but label_width is set to " << param_.label_width;
diff --git a/src/io/iter_image_recordio_2.cc b/src/io/iter_image_recordio_2.cc
index b6ff6e99b034..846d1abccbb5 100644
--- a/src/io/iter_image_recordio_2.cc
+++ b/src/io/iter_image_recordio_2.cc
@@ -303,7 +303,7 @@ inline bool ImageRecordIOParser2<DType>::ParseNext(DataBatch *out) {
         if (!legacy_shuffle_) {
           n_to_out = ParseChunk(data_dptr, label_dptr, current_size, &chunk);
         } else {
-          n_to_out = ParseChunk(NULL, NULL, batch_param_.batch_size, &chunk);
+          n_to_out = ParseChunk(nullptr, nullptr, batch_param_.batch_size, &chunk);
         }
         // Count number of parsed images that do not fit into current out
         n_parsed_ = inst_order_.size();
@@ -542,7 +542,7 @@ inline unsigned ImageRecordIOParser2<DType>::ParseChunk(DType* data_dptr, real_t
       std::vector<float> label_buf;
       if (label_map_ != nullptr) {
         label_buf = label_map_->FindCopy(rec.image_index());
-      } else if (rec.label != NULL) {
+      } else if (rec.label != nullptr) {
         CHECK_EQ(param_.label_width, rec.num_label)
           << "rec file provide " << rec.num_label << "-dimensional label "
              "but label_width is set to " << param_.label_width;
@@ -624,7 +624,7 @@ inline void ImageRecordIOParser2<DType>::CreateMeanImg(void) {
     while (source_->NextChunk(&chunk)) {
       inst_order_.clear();
       // Parse chunk w/o putting anything in out
-      ParseChunk(NULL, NULL, batch_param_.batch_size, &chunk);
+      ParseChunk(nullptr, nullptr, batch_param_.batch_size, &chunk);
       for (unsigned i = 0; i < inst_order_.size(); ++i) {
         std::pair<unsigned, unsigned> place = inst_order_[i];
         mshadow::Tensor<cpu, 3> outimg =
diff --git a/src/io/iter_mnist.cc b/src/io/iter_mnist.cc
index 1882a560d55f..40223472c96c 100644
--- a/src/io/iter_mnist.cc
+++ b/src/io/iter_mnist.cc
@@ -80,11 +80,11 @@ struct MNISTParam : public dmlc::Parameter<MNISTParam> {
 class MNISTIter: public IIterator<TBlobBatch> {
  public:
   MNISTIter(void) : loc_(0), inst_offset_(0) {
-    img_.dptr_ = NULL;
+    img_.dptr_ = nullptr;
     out_.data.resize(2);
   }
   virtual ~MNISTIter(void) {
-    if (img_.dptr_ != NULL) delete []img_.dptr_;
+    if (img_.dptr_ != nullptr) delete []img_.dptr_;
   }
   // intialize iterator loads data in
   virtual void Init(const std::vector<std::pair<std::string, std::string> >& kwargs) {
diff --git a/src/ndarray/ndarray.cc b/src/ndarray/ndarray.cc
index ddffa28cfd31..b443d5d318cf 100644
--- a/src/ndarray/ndarray.cc
+++ b/src/ndarray/ndarray.cc
@@ -2046,7 +2046,7 @@ void Imdecode(NDArray *ret, NDArray mean, size_t index,
 #if MXNET_USE_OPENCV
   cv::Mat buf(1, size, CV_8U, str_img);
   cv::Mat res = cv::imdecode(buf, n_channels == 1 ? 0 : -1);
-  CHECK(res.data != NULL) << "OpenCV Failed to decode image";
+  CHECK(res.data != nullptr) << "OpenCV Failed to decode image";
   CHECK_LE(n_channels, static_cast<size_t>(res.channels()));
   if (y1 - y0 == 0) {
     x0 = 0;
diff --git a/src/operator/bilinear_sampler.cc b/src/operator/bilinear_sampler.cc
index a3b7d5764245..c435fdeca481 100644
--- a/src/operator/bilinear_sampler.cc
+++ b/src/operator/bilinear_sampler.cc
@@ -163,7 +163,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator* CreateOp<cpu>(BilinearSamplerParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new BilinearSamplerOp<cpu, DType>(param);
   })
diff --git a/src/operator/contrib/count_sketch.cc b/src/operator/contrib/count_sketch.cc
index 12814116bbf4..ca239b63246f 100644
--- a/src/operator/contrib/count_sketch.cc
+++ b/src/operator/contrib/count_sketch.cc
@@ -30,7 +30,7 @@ namespace op {
 template<>
 Operator *CreateOp<cpu>(CountSketchParam param, int dtype) {
     LOG(FATAL) << "CountSketch is only available for GPU.";
-    return NULL;
+    return nullptr;
 }
 Operator *CountSketchProp::CreateOperatorEx(Context ctx, std::vector<TShape> *in_shape,
                                             std::vector<int> *in_type) const {
diff --git a/src/operator/contrib/deformable_convolution.cc b/src/operator/contrib/deformable_convolution.cc
index 352baa12fbc1..78a7a1250d3c 100644
--- a/src/operator/contrib/deformable_convolution.cc
+++ b/src/operator/contrib/deformable_convolution.cc
@@ -36,7 +36,7 @@ Operator* CreateOp<cpu>(DeformableConvolutionParam param, int dtype,
                         std::vector<TShape> *in_shape,
                         std::vector<TShape> *out_shape,
                         Context ctx) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new DeformableConvolutionOp<cpu, DType>(param);
   })
diff --git a/src/operator/contrib/deformable_psroi_pooling.cc b/src/operator/contrib/deformable_psroi_pooling.cc
index 42cf6f19df30..6aaf607f059a 100644
--- a/src/operator/contrib/deformable_psroi_pooling.cc
+++ b/src/operator/contrib/deformable_psroi_pooling.cc
@@ -81,7 +81,7 @@ namespace op {
 
   template<>
   Operator *CreateOp<cpu>(DeformablePSROIPoolingParam param, int dtype) {
-    Operator* op = NULL;
+    Operator* op = nullptr;
     MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
       op = new DeformablePSROIPoolingOp<cpu, DType>(param);
     });
diff --git a/src/operator/contrib/deformable_psroi_pooling.cu b/src/operator/contrib/deformable_psroi_pooling.cu
index 71bbd4cd7f2a..bf7d1c0bc755 100644
--- a/src/operator/contrib/deformable_psroi_pooling.cu
+++ b/src/operator/contrib/deformable_psroi_pooling.cu
@@ -423,7 +423,7 @@ namespace op {
 
   template<>
   Operator* CreateOp<gpu>(DeformablePSROIPoolingParam param, int dtype) {
-    Operator* op = NULL;
+    Operator* op = nullptr;
     MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
       op = new DeformablePSROIPoolingOp<gpu, DType>(param);
     });
diff --git a/src/operator/contrib/fft.cc b/src/operator/contrib/fft.cc
index 8332451bf921..4a4395836e3f 100644
--- a/src/operator/contrib/fft.cc
+++ b/src/operator/contrib/fft.cc
@@ -30,7 +30,7 @@ namespace op {
 template<>
 Operator *CreateOp<cpu>(FFTParam param, int dtype) {
   LOG(FATAL) << "fft is only available for GPU.";
-  return NULL;
+  return nullptr;
 }
 
 Operator *FFTProp::CreateOperatorEx(Context ctx, std::vector<TShape> *in_shape,
diff --git a/src/operator/contrib/ifft.cc b/src/operator/contrib/ifft.cc
index 26e7041ce02f..cb4605d8b787 100644
--- a/src/operator/contrib/ifft.cc
+++ b/src/operator/contrib/ifft.cc
@@ -31,7 +31,7 @@ namespace op {
 template<>
 Operator *CreateOp<cpu>(IFFTParam param, int dtype) {
   LOG(FATAL) << "ifft is only available for GPU.";
-  return NULL;
+  return nullptr;
 }
 
 Operator *IFFTProp::CreateOperatorEx(Context ctx, std::vector<TShape> *in_shape,
diff --git a/src/operator/contrib/multibox_detection.cc b/src/operator/contrib/multibox_detection.cc
index f92460e9e5e9..c005dfa06590 100644
--- a/src/operator/contrib/multibox_detection.cc
+++ b/src/operator/contrib/multibox_detection.cc
@@ -198,7 +198,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<cpu>(MultiBoxDetectionParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new MultiBoxDetectionOp<cpu, DType>(param);
   });
diff --git a/src/operator/contrib/multibox_prior.cc b/src/operator/contrib/multibox_prior.cc
index 22a9c10cd958..579ea608aa9f 100644
--- a/src/operator/contrib/multibox_prior.cc
+++ b/src/operator/contrib/multibox_prior.cc
@@ -76,7 +76,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator* CreateOp<cpu>(MultiBoxPriorParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new MultiBoxPriorOp<cpu, DType>(param);
   });
diff --git a/src/operator/contrib/multibox_target.cc b/src/operator/contrib/multibox_target.cc
index 2fa041dd34cf..093234b59ec3 100644
--- a/src/operator/contrib/multibox_target.cc
+++ b/src/operator/contrib/multibox_target.cc
@@ -284,7 +284,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<cpu>(MultiBoxTargetParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new MultiBoxTargetOp<cpu, DType>(param);
   });
diff --git a/src/operator/contrib/psroi_pooling.cc b/src/operator/contrib/psroi_pooling.cc
index 75b533446b8e..d3a3871ed004 100644
--- a/src/operator/contrib/psroi_pooling.cc
+++ b/src/operator/contrib/psroi_pooling.cc
@@ -66,7 +66,7 @@ namespace op {
 
 template<>
 Operator *CreateOp<cpu>(PSROIPoolingParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new PSROIPoolingOp<cpu, DType>(param);
   });
diff --git a/src/operator/contrib/psroi_pooling.cu b/src/operator/contrib/psroi_pooling.cu
index 472131637461..e4de9248dfbf 100644
--- a/src/operator/contrib/psroi_pooling.cu
+++ b/src/operator/contrib/psroi_pooling.cu
@@ -268,7 +268,7 @@ namespace op {
 
 template<>
 Operator* CreateOp<gpu>(PSROIPoolingParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new PSROIPoolingOp<gpu, DType>(param);
   });
diff --git a/src/operator/convolution_v1.cc b/src/operator/convolution_v1.cc
index 86c0fbb33291..b6250a7a77f5 100644
--- a/src/operator/convolution_v1.cc
+++ b/src/operator/convolution_v1.cc
@@ -38,7 +38,7 @@ Operator* CreateOp<cpu>(ConvolutionV1Param param, int dtype,
                         std::vector<TShape> *in_shape,
                         std::vector<TShape> *out_shape,
                         Context ctx) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new ConvolutionV1Op<cpu, DType>(param);
   })
diff --git a/src/operator/correlation.cc b/src/operator/correlation.cc
index fe89e8462d12..d0c664ad4f9c 100644
--- a/src/operator/correlation.cc
+++ b/src/operator/correlation.cc
@@ -149,7 +149,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<cpu>(CorrelationParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new CorrelationOp<cpu, DType>(param);
   });
diff --git a/src/operator/correlation.cu b/src/operator/correlation.cu
index 6bc16cde5098..821b9007a8fe 100644
--- a/src/operator/correlation.cu
+++ b/src/operator/correlation.cu
@@ -622,7 +622,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator* CreateOp<gpu>(CorrelationParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new CorrelationOp<gpu, DType>(param);
   });
diff --git a/src/operator/custom/custom.cc b/src/operator/custom/custom.cc
index d117a2842166..4cda1375fd29 100644
--- a/src/operator/custom/custom.cc
+++ b/src/operator/custom/custom.cc
@@ -75,12 +75,12 @@ inline void AllocateNDArrayCopy(NDArray** nd,
 template<CustomOpPropCallbacks Type>
 std::vector<std::string> List(const NodeAttrs& attrs) {
   const CustomParam& params = nnvm::get<CustomParam>(attrs.parsed);
-  char ** args = NULL;
+  char ** args = nullptr;
   CHECK(reinterpret_cast<CustomOpListFunc>(
     params.info->callbacks[Type])(
       &args, params.info->contexts[Type]));
   std::vector<std::string> ret;
-  for (int i = 0; args[i] != NULL; ++i) {
+  for (int i = 0; args[i] != nullptr; ++i) {
     ret.push_back(args[i]);
   }
   return ret;
diff --git a/src/operator/grid_generator.cc b/src/operator/grid_generator.cc
index ea6e66145c4a..96ec5d5a7e7a 100644
--- a/src/operator/grid_generator.cc
+++ b/src/operator/grid_generator.cc
@@ -30,7 +30,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator* CreateOp<cpu>(GridGeneratorParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   if (dtype == mshadow::kFloat32) {
     op = new GridGeneratorOp<cpu, float>(param);
   } else {
diff --git a/src/operator/l2_normalization.cc b/src/operator/l2_normalization.cc
index c313b4424423..f2f485ae6d1b 100644
--- a/src/operator/l2_normalization.cc
+++ b/src/operator/l2_normalization.cc
@@ -27,7 +27,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator* CreateOp<cpu>(L2NormalizationParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new L2NormalizationOp<cpu, DType>(param);
   });
diff --git a/src/operator/l2_normalization.cu b/src/operator/l2_normalization.cu
index 2034f984174d..e5157811d894 100644
--- a/src/operator/l2_normalization.cu
+++ b/src/operator/l2_normalization.cu
@@ -27,7 +27,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator* CreateOp<gpu>(L2NormalizationParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new L2NormalizationOp<gpu, DType>(param);
   });
diff --git a/src/operator/leaky_relu.cc b/src/operator/leaky_relu.cc
index 4bb24237b8ed..45f9511c9085 100644
--- a/src/operator/leaky_relu.cc
+++ b/src/operator/leaky_relu.cc
@@ -31,7 +31,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<cpu>(LeakyReLUParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new LeakyReLUOp<cpu, DType>(param);
   });
diff --git a/src/operator/leaky_relu.cu b/src/operator/leaky_relu.cu
index 74b444d87597..a2e0e959a15b 100644
--- a/src/operator/leaky_relu.cu
+++ b/src/operator/leaky_relu.cu
@@ -30,7 +30,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<gpu>(LeakyReLUParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new LeakyReLUOp<gpu, DType>(param);
   });
diff --git a/src/operator/make_loss.cc b/src/operator/make_loss.cc
index 14304d3cc263..7e45f4ce4ff4 100644
--- a/src/operator/make_loss.cc
+++ b/src/operator/make_loss.cc
@@ -28,7 +28,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<cpu>(MakeLossParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new MakeLossOp<cpu, DType>(param);
   });
diff --git a/src/operator/pad.cc b/src/operator/pad.cc
index 2332c93b8d5b..6c66b29082c4 100644
--- a/src/operator/pad.cc
+++ b/src/operator/pad.cc
@@ -668,7 +668,7 @@ namespace mxnet {
 namespace op {
 template <>
 Operator *CreateOp<cpu>(PadParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, { op = new PadOp<cpu, DType>(param); })
   return op;
 }
diff --git a/src/operator/pooling_v1.cc b/src/operator/pooling_v1.cc
index 5b68a08db602..afb51d762ddd 100644
--- a/src/operator/pooling_v1.cc
+++ b/src/operator/pooling_v1.cc
@@ -30,7 +30,7 @@ namespace op {
 
 template<>
 Operator *CreateOp<cpu>(PoolingV1Param param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     switch (param.pool_type) {
       case pool_v1_enum::kMaxPooling:
@@ -44,7 +44,7 @@ Operator *CreateOp<cpu>(PoolingV1Param param, int dtype) {
         break;
       default:
         LOG(FATAL) << "unknown pooling type";
-        return NULL;
+        return nullptr;
     }
   })
 
diff --git a/src/operator/rnn.cc b/src/operator/rnn.cc
index 73ef4f0f42a7..9ba764904e15 100644
--- a/src/operator/rnn.cc
+++ b/src/operator/rnn.cc
@@ -29,7 +29,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<cpu>(RNNParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new RNNOp<DType>(param);
   });
diff --git a/src/operator/roi_pooling.cc b/src/operator/roi_pooling.cc
index 124d811c46a0..7f15dcb406dc 100644
--- a/src/operator/roi_pooling.cc
+++ b/src/operator/roi_pooling.cc
@@ -234,7 +234,7 @@ namespace op {
 
 template<>
 Operator *CreateOp<cpu>(ROIPoolingParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new ROIPoolingOp<cpu, DType>(param);
   });
diff --git a/src/operator/roi_pooling.cu b/src/operator/roi_pooling.cu
index 066c2ffd0635..9ea99b309aaf 100644
--- a/src/operator/roi_pooling.cu
+++ b/src/operator/roi_pooling.cu
@@ -264,7 +264,7 @@ namespace op {
 
 template<>
 Operator* CreateOp<gpu>(ROIPoolingParam param, int dtype) {
-  Operator* op = NULL;
+  Operator* op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new ROIPoolingOp<gpu, DType>(param);
   });
diff --git a/src/operator/sequence_last.cc b/src/operator/sequence_last.cc
index f87400b21f94..345524b38134 100644
--- a/src/operator/sequence_last.cc
+++ b/src/operator/sequence_last.cc
@@ -29,7 +29,7 @@ namespace mxnet {
 namespace op {
 template <>
 Operator *CreateOp<cpu>(SequenceLastParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_TYPE_SWITCH(dtype, DType,
                            { op = new SequenceLastOp<cpu, DType>(param); })
   return op;
diff --git a/src/operator/sequence_mask.cc b/src/operator/sequence_mask.cc
index 047634cc7bcd..e02c57bfd917 100644
--- a/src/operator/sequence_mask.cc
+++ b/src/operator/sequence_mask.cc
@@ -29,7 +29,7 @@ namespace mxnet {
 namespace op {
 template <>
 Operator *CreateOp<cpu>(SequenceMaskParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_TYPE_SWITCH(dtype, DType,
                            { op = new SequenceMaskOp<cpu, DType>(param); })
   return op;
diff --git a/src/operator/sequence_reverse.cc b/src/operator/sequence_reverse.cc
index 834e4f401ede..21cab7891101 100644
--- a/src/operator/sequence_reverse.cc
+++ b/src/operator/sequence_reverse.cc
@@ -29,7 +29,7 @@ namespace mxnet {
 namespace op {
 template <>
 Operator *CreateOp<cpu>(SequenceReverseParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_TYPE_SWITCH(dtype, DType,
                            { op = new SequenceReverseOp<cpu, DType>(param); })
   return op;
diff --git a/src/operator/sequence_reverse.cu b/src/operator/sequence_reverse.cu
index 9c1574814a16..1edc9c13d493 100644
--- a/src/operator/sequence_reverse.cu
+++ b/src/operator/sequence_reverse.cu
@@ -29,7 +29,7 @@
 namespace mxnet {
 namespace op {
 template <> Operator *CreateOp<gpu>(SequenceReverseParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_TYPE_SWITCH(dtype, DType, {
     op = new SequenceReverseOp<gpu, DType>(param);
   })
diff --git a/src/operator/softmax_output.cc b/src/operator/softmax_output.cc
index 27b3295654b9..5ba421fd195b 100644
--- a/src/operator/softmax_output.cc
+++ b/src/operator/softmax_output.cc
@@ -29,7 +29,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<cpu>(SoftmaxOutputParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new SoftmaxOutputOp<cpu, DType>(param);
   })
diff --git a/src/operator/spatial_transformer.cc b/src/operator/spatial_transformer.cc
index 8c6779df1b7a..2dcb427ef036 100644
--- a/src/operator/spatial_transformer.cc
+++ b/src/operator/spatial_transformer.cc
@@ -153,7 +153,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator* CreateOp<cpu>(SpatialTransformerParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new SpatialTransformerOp<cpu, DType>(param);
   })
diff --git a/src/operator/svm_output.cc b/src/operator/svm_output.cc
index c84c2af28483..a291f7298706 100644
--- a/src/operator/svm_output.cc
+++ b/src/operator/svm_output.cc
@@ -71,7 +71,7 @@ namespace mxnet {
 namespace op {
 template<>
 Operator *CreateOp<cpu>(SVMOutputParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_REAL_TYPE_SWITCH(dtype, DType, {
     op = new SVMOutputOp<cpu, DType>(param);
   })
diff --git a/src/operator/swapaxis.cc b/src/operator/swapaxis.cc
index 12bc52e1f6fd..b78062fde8be 100644
--- a/src/operator/swapaxis.cc
+++ b/src/operator/swapaxis.cc
@@ -31,7 +31,7 @@ namespace op {
 
 template<>
 Operator* CreateOp<cpu>(SwapAxisParam param, int dtype) {
-  Operator *op = NULL;
+  Operator *op = nullptr;
   MSHADOW_TYPE_SWITCH(dtype, DType, {
     op = new SwapAxisOp<cpu, DType>(param);
   });