return exception if modelname is empty (#4226)

Author: argzdev

firebase-ml-modeldownloader/src/main/java/com/google/firebase/ml/modeldownloader/internal/CustomModelDownloadService.java

@@ -16,6 +16,7 @@
 
 import android.content.Context;
 import android.content.pm.PackageManager;
+import android.text.TextUtils;
 import android.util.JsonReader;
 import android.util.Log;
 import androidx.annotation.NonNull;
@@ -148,6 +149,12 @@ public Task<CustomModel> getNewDownloadUrlWithExpiry(String projectNumber, Strin
   public Task<CustomModel> getCustomModelDetails(
       String projectNumber, String modelName, String modelHash) {
     try {
+
+      if (TextUtils.isEmpty(modelName))
+        throw new FirebaseMlException(
+            "Error cannot retrieve model from reading an empty modelName",
+            FirebaseMlException.INVALID_ARGUMENT);
+
       URL url =
           new URL(String.format(DOWNLOAD_MODEL_REGEX, downloadHost, projectNumber, modelName));
       HttpURLConnection connection = (HttpURLConnection) url.openConnection();
@@ -206,6 +213,8 @@ public Task<CustomModel> getCustomModelDetails(
           new FirebaseMlException(
               "Error reading custom model from download service: " + e.getMessage(),
               FirebaseMlException.INVALID_ARGUMENT));
+    } catch (FirebaseMlException e) {
+      return Tasks.forException(e);
     }
   }