diff --git a/core/src/main/scala/org/apache/spark/rdd/InputFileNameHolder.scala b/core/src/main/scala/org/apache/spark/rdd/InputFileNameHolder.scala
index f40d4c8e0a4d0e66f6fb06ce469ee6d41437b5bf..960c91a154db16bc7a79ea116773c02d04d05bb1 100644
--- a/core/src/main/scala/org/apache/spark/rdd/InputFileNameHolder.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/InputFileNameHolder.scala
@@ -22,6 +22,8 @@ import org.apache.spark.unsafe.types.UTF8String
 /**
  * This holds file names of the current Spark task. This is used in HadoopRDD,
  * FileScanRDD, NewHadoopRDD and InputFileName function in Spark SQL.
+ *
+ * The returned value should never be null but empty string if it is unknown.
  */
 private[spark] object InputFileNameHolder {
   /**
@@ -32,9 +34,15 @@ private[spark] object InputFileNameHolder {
     override protected def initialValue(): UTF8String = UTF8String.fromString("")
   }
 
+  /**
+   * Returns the holding file name or empty string if it is unknown.
+   */
   def getInputFileName(): UTF8String = inputFileName.get()
 
-  private[spark] def setInputFileName(file: String) = inputFileName.set(UTF8String.fromString(file))
+  private[spark] def setInputFileName(file: String) = {
+    require(file != null, "The input file name cannot be null")
+    inputFileName.set(UTF8String.fromString(file))
+  }
 
   private[spark] def unsetInputFileName(): Unit = inputFileName.remove()
 
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/InputFileName.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/InputFileName.scala
index b7fb285133bfcde67f8d84ea81b2709c7bf1aee4..d412336699d8011069bec284c296edbc006cf9bc 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/InputFileName.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/InputFileName.scala
@@ -30,7 +30,7 @@ import org.apache.spark.unsafe.types.UTF8String
   usage = "_FUNC_() - Returns the name of the current file being read if available.")
 case class InputFileName() extends LeafExpression with Nondeterministic {
 
-  override def nullable: Boolean = true
+  override def nullable: Boolean = false
 
   override def dataType: DataType = StringType