code: public KieServerHttpRequest contentType(final String contentType, final String charset ) {
          if( charset != null && charset.length() > 0 ) {
              final String separator = "; " + PARAM_CHARSET + '=';
              return header(CONTENT_TYPE, contentType + separator + charset);
          } else
              return header(CONTENT_TYPE, contentType);
      }
docs: Set the 'Content-Type' request header to the given value and charset
  
  @param contentType
  @param charset
  @return this request