code: public TransformTask setWriteMode(Target.WriteMode mode) {
      Preconditions.checkArgument(mode != Target.WriteMode.CHECKPOINT,
          "Checkpoint is not an allowed write mode");
      this.mode = mode;
      return this;
    }
docs: Set the output write mode: default, overwrite, or append.
  
  @param mode the output write mode
  @return this for method chaining