code: public void setCustomHttpHeader(String headerName, String headerValue) {
  		if(CONTENT_TYPE.equals(headerName) || HOST.equals(headerName)
  				|| CONTENT_LENGTH.equals(headerName)) {
  			throw new XMLRPCRuntimeException("You cannot modify the Host, Content-Type or Content-Length header.");
  		}
  		httpParameters.put(headerName, headerValue);
  	}
docs: Set a HTTP header field to a custom value.
  You cannot modify the Host or Content-Type field that way.
  If the field already exists, the old value is overwritten.
  
  @param headerName The name of the header field.
  @param headerValue The new value of the header field.