DATAREDIS-824 - Fix potential NPE in DefaultReactiveHashOperations when deserializing values.

Avoid ByteBuffer creation for null values indicating absent keys in hash.

Original Pull Request: #340

src/main/java/org/springframework/data/redis/core/DefaultReactiveHashOperations.java

@@ -277,7 +277,7 @@ class DefaultReactiveHashOperations<H, HK, HV> implements ReactiveHashOperations
 
 		List<HV> values = new ArrayList<>(source.size());
 		for (ByteBuffer byteBuffer : source) {
-			values.add(readHashValue(byteBuffer));
+			values.add(byteBuffer == null ? null : readHashValue(byteBuffer));
 		}
 		return values;
 	}