[SPARK-2331] SparkContext.emptyRDD should return RDD[T] not EmptyRDD[T]

Author: Reynold Xin <rxin@databricks.com>

Closes #10394 from rxin/SPARK-2331.

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -1248,7 +1248,7 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
   }
 
   /** Get an RDD that has no partitions or elements. */
-  def emptyRDD[T: ClassTag]: EmptyRDD[T] = new EmptyRDD[T](this)
+  def emptyRDD[T: ClassTag]: RDD[T] = new EmptyRDD[T](this)
 
   // Methods for creating shared variables
 

project/MimaExcludes.scala

@@ -34,6 +34,9 @@ import com.typesafe.tools.mima.core.ProblemFilters._
 object MimaExcludes {
   def excludes(version: String) = version match {
     case v if v.startsWith("2.0") =>
+      Seq(
+        ProblemFilters.exclude[IncompatibleResultTypeProblem]("org.apache.spark.SparkContext.emptyRDD")
+        ) ++
       // When 1.6 is officially released, update this exclusion list.
       Seq(
         MimaBuild.excludeSparkPackage("deploy"),