code: @Override
      public void close() {
          if (mIsClosed) {
              return;
          }
          mIsClosed = true;
  
          mRetrofit = null;
          mRetrofitService = null;
          mRequestSignatorInterceptor = null;
          mHttpLoggingInterceptor = null;
  
          mApplicationContext.clear();
          mApplicationContext = null;
  
          mClientKey = null;
      }
docs: Release resources associated with this client.
  <p/>
  {@inheritDoc}