Fix includes

src/access/ProviderDeviceTypeResolver.h

@@ -32,10 +32,6 @@ class DynamicProviderDeviceTypeResolver : public chip::Access::AccessControl::De
     bool IsDeviceTypeOnEndpoint(chip::DeviceTypeId deviceType, chip::EndpointId endpoint) override
     {
         auto it = mModelGetter()->GetDeviceTypes(endpoint);
-        if (!it)
-        {
-            return false;
-        }
         for (auto type = it->Next(); type.has_value(); type = it->Next())
         {
             if (type->deviceTypeId == deviceType)

src/app/clusters/descriptor/descriptor.cpp

@@ -156,11 +156,6 @@ CHIP_ERROR DescriptorAttrAccess::ReadDeviceAttribute(EndpointId endpoint, Attrib
 {
     CHIP_ERROR err = aEncoder.EncodeList([&endpoint](const auto & encoder) -> CHIP_ERROR {
         auto it = InteractionModelEngine::GetInstance()->GetDataModelProvider()->GetDeviceTypes(endpoint);
-        if (!it)
-        {
-            return CHIP_NO_ERROR;
-        }
-
         for (auto deviceType = it->Next(); deviceType.has_value(); deviceType = it->Next())
         {
             Descriptor::Structs::DeviceTypeStruct::Type deviceStruct;

src/app/clusters/descriptor/descriptor.h

@@ -14,6 +14,8 @@
  *    limitations under the License.
  */
 
+#include <cstdint>
+
 namespace chip {
 namespace app {
 namespace Clusters {

src/app/data-model-provider/Iterators.h

@@ -74,18 +74,19 @@ class MetaDataIterator : public FastForwardIterator<T>
 };
 
 template <typename T>
-class NullFastForwardIterator : public FastForwardIterator<T>
+class NullElementIterator : public ElementIterator<T>
 {
 public:
     std::optional<T> Next() override { return std::nullopt; }
-    bool SeekTo(const T & value) override { return false; }
 };
 
 /// Null iterator, generally just used for tests
 template <typename T, typename Meta>
-class NullMetadataIterator : public NullFastForwardIterator<T>
+class NullMetadataIterator : public MetaDataIterator<T, Meta>
 {
 public:
+    std::optional<T> Next() override { return std::nullopt; }
+    bool SeekTo(const T & value) override { return false; }
     std::optional<Meta> GetMetadata() override { return std::nullopt; }
 };
 

src/app/data-model-provider/MetadataTypes.h

@@ -17,6 +17,7 @@
 #pragma once
 
 #include <cstdint>
+#include <memory>
 #include <optional>
 
 #include <access/Privilege.h>
@@ -192,27 +193,51 @@ class ProviderMetadataTree
     //    tight loop/operation within event loop processing and SHOULD NOT be
     //    stored for use across execution boundaries
     //
+    // RETURN VALUES
+    //
+    //  - These MUST NOT return null pointer. Use NullIterators if empty data sets
+    //    are to be returned.
+    //
     // PERFORMANCE
     //
     //  - Lookups should be performed using `Get...` and `SeekTo`.
     //
     /////////////////////////////////////////////////////////////////////////
-    virtual std::unique_ptr<MetaDataIterator<EndpointId, EndpointInfo>> GetEndpoints() { return nullptr; }
-    virtual std::unique_ptr<ElementIterator<DeviceTypeEntry>> GetDeviceTypes(EndpointId endpointId) { return nullptr; }
-    virtual std::unique_ptr<ElementIterator<SemanticTag>> GetSemanticTags(EndpointId endpointId) { return nullptr; }
+    virtual std::unique_ptr<MetaDataIterator<EndpointId, EndpointInfo>> GetEndpoints()
+    {
+        return std::make_unique<NullMetadataIterator<EndpointId, EndpointInfo>>();
+    }
+    virtual std::unique_ptr<ElementIterator<DeviceTypeEntry>> GetDeviceTypes(EndpointId endpointId)
+    {
+        return std::make_unique<NullElementIterator<DeviceTypeEntry>>();
+    }
+    virtual std::unique_ptr<ElementIterator<SemanticTag>> GetSemanticTags(EndpointId endpointId)
+    {
+        return std::make_unique<NullElementIterator<SemanticTag>>();
+    }
 
-    virtual std::unique_ptr<MetaDataIterator<ClusterId, ClusterInfo>> GetServerClusters(EndpointId endpointId) { return nullptr; }
-    virtual std::unique_ptr<ElementIterator<ClusterId>> GetClientClusters(EndpointId endpointId) { return nullptr; }
+    virtual std::unique_ptr<MetaDataIterator<ClusterId, ClusterInfo>> GetServerClusters(EndpointId endpointId)
+    {
+        return std::make_unique<NullMetadataIterator<ClusterId, ClusterInfo>>();
+    }
+
+    virtual std::unique_ptr<ElementIterator<ClusterId>> GetClientClusters(EndpointId endpointId)
+    {
+        return std::make_unique<NullElementIterator<ClusterId>>();
+    }
 
     virtual std::unique_ptr<MetaDataIterator<AttributeId, AttributeInfo>> GetAttributes(ConcreteClusterPath clusterPath)
     {
-        return nullptr;
+        return std::make_unique<NullMetadataIterator<AttributeId, AttributeInfo>>();
     }
     virtual std::unique_ptr<MetaDataIterator<CommandId, CommandInfo>> GetAcceptedCommands(ConcreteClusterPath clusterPath)
     {
-        return nullptr;
+        return std::make_unique<NullMetadataIterator<CommandId, CommandInfo>>();
+    }
+    virtual std::unique_ptr<ElementIterator<CommandId>> GetGeneratedCommands(ConcreteClusterPath clusterPath)
+    {
+        return std::make_unique<NullElementIterator<CommandId>>();
     }
-    virtual std::unique_ptr<ElementIterator<CommandId>> GetGeneratedCommands(ConcreteClusterPath clusterPath) { return nullptr; }
 
     // This iteration will list all the endpoints in the data model
     virtual EndpointEntry FirstEndpoint()                              = 0;

src/data-model-providers/codegen/CodegenDataModelProvider.cpp

@@ -887,7 +887,7 @@ CodegenDataModelProvider::GetDeviceTypes(EndpointId endpointId)
     std::optional<unsigned> endpoint_index = TryFindEndpointIndex(endpointId);
     if (!endpoint_index.has_value())
     {
-        return nullptr;
+        return std::make_unique<DataModel::NullElementIterator<DataModel::DeviceTypeEntry>>();
     }
 
     CHIP_ERROR err = CHIP_NO_ERROR;