Fix NPE when metadata is null in MilvusVectorStore

Adds a null check before injecting the distance property into metadata to prevent a NullPointerException if metadata is missing from the row record.

Signed-off-by: little_huang <[email protected]>

Author: little-huang

vector-stores/spring-ai-milvus-store/src/main/java/org/springframework/ai/vectorstore/milvus/MilvusVectorStore.java

@@ -379,8 +379,10 @@ public List<Document> doSimilaritySearch(SearchRequest request) {
 				JsonObject metadata = new JsonObject();
 				try {
 					metadata = (JsonObject) rowRecord.get(this.metadataFieldName);
-					// inject the distance into the metadata.
-					metadata.addProperty(DocumentMetadata.DISTANCE.value(), 1 - getResultSimilarity(rowRecord));
+					if (metadata != null) {
+						// inject the distance into the metadata.
+						metadata.addProperty(DocumentMetadata.DISTANCE.value(), 1 - getResultSimilarity(rowRecord));
+					}
 				}
 				catch (ParamException e) {
 					// skip the ParamException if metadata doesn't exist for the custom