docs: public String getStringBody() throws BoxException {
          if (mBodyString != null) {
              return mBodyString;
          }
  
          InputStream stream = null;
          try {
              stream = isErrorCode(this.mResponseCode) ?
                      mConnection.getErrorStream() :
                      mConnection.getInputStream();
              mBodyString = readStream(stream);
          } catch (IOException e) {
              throw new BoxException("Unable to get string body", e);
          }
          return mBodyString;
      }