docs: public RecipientDsnFields withExtensionFields(ExtensionField... extensionFields) {
          if (this.extensionFields == null) {
              setExtensionFields(new com.amazonaws.internal.SdkInternalList<ExtensionField>(extensionFields.length));
          }
          for (ExtensionField ele : extensionFields) {
              this.extensionFields.add(ele);
          }
          return this;
      }