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

val jsc = new org.apache.spark.api.java.JavaSparkContext(sc)
val jhc = new org.apache.spark.sql.hive.api.java.JavaHiveContext(jsc)
val nrdd = jhc.hql("select null from spark_test.for_test")
println(nrdd.schema)
Then the error is thrown as follows:
scala.MatchError: NullType (of class org.apache.spark.sql.catalyst.types.NullType$)
at org.apache.spark.sql.types.util.DataTypeConversions$.asJavaDataType(DataTypeConversions.scala:43)

Author: YanTangZhai <hakeemzhai@tencent.com>
Author: yantangzhai <tyz0303@163.com>
Author: Michael Armbrust <michael@databricks.com>

Closes #3538 from YanTangZhai/MatchNullType and squashes the following commits:

e052dff [yantangzhai] [SPARK-4676] [SQL] JavaSchemaRDD.schema may throw NullType MatchError if sql has null
4b4bb34 [yantangzhai] [SPARK-4676] [SQL] JavaSchemaRDD.schema may throw NullType MatchError if sql has null
896c7b7 [yantangzhai] fix NullType MatchError in JavaSchemaRDD when sql has null
6e643f8 [YanTangZhai] Merge pull request #11 from apache/master
e249846 [YanTangZhai] Merge pull request #10 from apache/master
d26d982 [YanTangZhai] Merge pull request #9 from apache/master
76d4027 [YanTangZhai] Merge pull request #8 from apache/master
03b62b0 [YanTangZhai] Merge pull request #7 from apache/master
8a00106 [YanTangZhai] Merge pull request #6 from apache/master
cbcba66 [YanTangZhai] Merge pull request #3 from apache/master
cdef539 [YanTangZhai] Merge pull request #1 from apache/master

(cherry picked from commit 1066427)
Signed-off-by: Michael Armbrust <michael@databricks.com>

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/package.scala

@@ -263,6 +263,16 @@ package object sql {
   @DeveloperApi
   val ShortType = catalyst.types.ShortType
 
+  /**
+   * :: DeveloperApi ::
+   *
+   * The data type representing `NULL` values.
+   *
+   * @group dataType
+   */
+  @DeveloperApi
+  val NullType = catalyst.types.NullType
+  
   /**
    * :: DeveloperApi ::
    *

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

@@ -62,6 +62,7 @@ protected[sql] object DataTypeConversions {
     case IntegerType => JDataType.IntegerType
     case LongType => JDataType.LongType
     case ShortType => JDataType.ShortType
+    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("")