docs: public void setRequestProperty(String pKey, String pValue) {
          if (connected) {
              throw new IllegalAccessError("Already connected");
          }
          String oldValue = requestProperties.getProperty(pKey);
  
          if (oldValue == null) {
              requestProperties.setProperty(pKey, pValue);
          }
          else {
              requestProperties.setProperty(pKey, oldValue + ", " + pValue);
          }
      }