handle zero models

Author: davidkyle

x-pack/plugin/inference/qa/inference-service-tests/src/javaRestTest/java/org/elasticsearch/xpack/inference/InferenceCrudIT.java

@@ -24,6 +24,7 @@
 import java.util.stream.Stream;
 
 import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.equalToIgnoringCase;
 import static org.hamcrest.Matchers.hasSize;
@@ -326,4 +327,9 @@ public void testSupportedStream() throws Exception {
             deleteModel(modelId);
         }
     }
+
+    public void testGetZeroModels() throws IOException {
+        var models = getModels("_all", TaskType.RERANK);
+        assertThat(models, empty());
+    }
 }

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/action/TransportGetInferenceModelAction.java

@@ -126,6 +126,11 @@ private void getModelsByTaskType(TaskType taskType, ActionListener<GetInferenceM
     }
 
     private void parseModels(List<UnparsedModel> unparsedModels, ActionListener<GetInferenceModelAction.Response> listener) {
+        if (unparsedModels.isEmpty()) {
+            listener.onResponse(new GetInferenceModelAction.Response(List.of()));
+            return;
+        }
+
         var parsedModelsByService = new HashMap<String, List<Model>>();
         try {
             for (var unparsedModel : unparsedModels) {