code: public HttpRequest withHeader(NottableString name, NottableString... values) {
          this.headers.withEntry(header(name, values));
          return this;
      }
docs: Adds one header to match on or to not match on using the NottableString, each NottableString can either be a positive matching value,
  such as string("match"), or a value to not match on, such as not("do not match"), the string values passed to the NottableString
  can also be a plain string or a regex (for more details of the supported regex syntax
  see http://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html)
  
  @param name   the header name as a NottableString
  @param values the header values which can be a varags of NottableStrings