bug fix for map type

Signed-off-by: yuye-aws <[email protected]>

src/main/java/org/opensearch/neuralsearch/processor/DocumentChunkingProcessor.java

@@ -153,8 +153,7 @@ private void validateContent(Object content, String inputField) {
                     );
                 }
             }
-        }
-        if (!(content instanceof String)) {
+        } else if (!(content instanceof String)) {
             throw new IllegalArgumentException(
                 "input field ["
                     + inputField