Handle dataPath = null case (#15326)

### Summary
Handle dataPath = null case
### Test plan
CI

Author: kirklandsign

extension/android/executorch_android/src/main/java/org/pytorch/executorch/extension/llm/LlmModule.java

@@ -70,7 +70,12 @@ public LlmModule(
    */
   public LlmModule(
       int modelType, String modulePath, String tokenizerPath, float temperature, String dataPath) {
-    this(modelType, modulePath, tokenizerPath, temperature, List.of(dataPath));
+    this(
+        modelType,
+        modulePath,
+        tokenizerPath,
+        temperature,
+        dataPath != null ? List.of(dataPath) : List.of());
   }
 
   /** Constructs a LLM Module for a model with given model path, tokenizer, temperature. */