Update src/main/java/org/opensearch/neuralsearch/util/ProcessorDocumentUtils.java

Co-authored-by: Martin Gaievski <gaievski@amazon.com>
Signed-off-by: zane-neo <zaniu@amazon.com>

Author: zane-neo

src/main/java/org/opensearch/neuralsearch/util/ProcessorDocumentUtils.java

@@ -58,7 +58,10 @@ private static void validateMapTypeValue(
         final Environment environment,
         final boolean allowEmpty
     ) {
-        if (sourceValue == null) return; // allow map type value to be null.
+        // allow map type value to be null
+        if (Objects.isNull(sourceValue) {
+             return; 
+        }
         validateDepth(sourceKey, depth, indexName, clusterService, environment);
         if (!(fieldMap instanceof Map)) { // source value is map type means configuration has to be map type
             throw new IllegalArgumentException(