few nits

sql/api/src/main/scala/org/apache/spark/sql/streaming/StatefulProcessorHandle.scala

@@ -52,6 +52,12 @@ private[sql] trait StatefulProcessorHandle extends Serializable {
   /**
    * Creates new or returns existing map state associated with stateName.
    * The MapState persists Key-Value pairs of type [K, V].
+   *
+   * @param stateName  - name of the state variable
+   * @param userKeyEnc  - spark sql encoder for the map key
+   * @tparam K - type of key for map state variable
+   * @tparam V - type of value for map state variable
+   * @return - instance of MapState of type [K,V] that can be used to store state persistently
    */
   def getMapState[K, V](stateName: String, userKeyEnc: Encoder[K]): MapState[K, V]
 

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/MapStateImpl.scala

@@ -49,7 +49,7 @@ class MapStateImpl[K, V](
   /** Get the state value if it exists */
   override def getValue(key: K): V = {
     // TODO do we want to reuse this function,
-    // or create a new error for user key?
+    // or create a new error for null user key?
     StateStoreErrors.requireNonNullStateValue(key, stateName)
     val encodedCompositeKey = stateTypesEncoder.encodeCompositeKey(key)
     val unsafeRowValue = store.get(encodedCompositeKey, stateName)

sql/core/src/test/scala/org/apache/spark/sql/streaming/TransformWithMapStateSuite.scala

@@ -114,7 +114,7 @@ class TransformWithMapStateSuite extends StreamTest {
 
       testStream(result, OutputMode.Update())(
         AddData(inputData, InputMapRow("k1", "getValue", ("v1", ""))),
-        CheckAnswer(("k1", "v1", "null"))
+        CheckAnswer(("k1", "v1", null))
       )
     }
   }