[SPARK-4676] [SQL] JavaSchemaRDD.schema may throw NullType MatchError if sql has null

Author: YanTangZhai

sql/core/src/main/java/org/apache/spark/sql/api/java/DataType.java

@@ -82,6 +82,11 @@ public abstract class DataType {
    */
   public static final ShortType ShortType = new ShortType();
 
+	/**
+	 * Gets the NullType object.
+	 */
+	public static final NullType NullType = new NullType();
+
   /**
    * Creates an ArrayType by specifying the data type of elements ({@code elementType}).
    * The field of {@code containsNull} is set to {@code true}.

sql/core/src/main/java/org/apache/spark/sql/api/java/NullType.java

@@ -0,0 +1,27 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.api.java;
+
+/**
+ * The data type representing null and NULL values.
+ *
+ * {@code NullType} is represented by the singleton object {@link DataType#NullType}.
+ */
+public class NullType extends DataType {
+  protected NullType() {}
+}

sql/core/src/main/scala/org/apache/spark/sql/types/util/DataTypeConversions.scala

@@ -62,7 +62,7 @@ protected[sql] object DataTypeConversions {
     case IntegerType => JDataType.IntegerType
     case LongType => JDataType.LongType
     case ShortType => JDataType.ShortType
-    case NullType => JDataType.StringType
+    case NullType => JDataType.NullType
 
     case arrayType: ArrayType => JDataType.createArrayType(
         asJavaDataType(arrayType.elementType), arrayType.containsNull)

sql/core/src/test/scala/org/apache/spark/sql/api/java/JavaSQLSuite.scala

@@ -68,6 +68,22 @@ class JavaSQLSuite extends FunSuite {
     javaSqlCtx.sql("SELECT * FROM people").collect()
   }
 
+	test("schema with null from JavaBeans") {
+	  val person = new PersonBean
+		person.setName("Michael")
+		person.setAge(29)
+
+		val rdd = javaCtx.parallelize(person :: Nil)
+		val schemaRDD = javaSqlCtx.applySchema(rdd, classOf[PersonBean])
+
+		schemaRDD.registerTempTable("people")
+		val nullRDD = javaSqlCtx.sql("SELECT null FROM people")
+		val structFields = nullRDD.schema.getFields()
+		assert(structFields.size == 1)
+		assert(structFields(0).getDataType().isInstanceOf[NullType])
+		assert(nullRDD.collect.head.row === Seq(null))
+	}
+
   test("all types in JavaBeans") {
     val bean = new AllTypesBean
     bean.setStringField("")