docs: public void setHeader(String name, String value) {
  //		int pos = 0;
  //		int crlfpos = 0;
          Pattern pattern = null;
  
          if (getHeaders(name) == null && value != null) {
              // header value not found, append to end
              addHeader(name, value);
          } else {
              pattern = getHeaderRegex(name);
              Matcher matcher = pattern.matcher(mMsgHeader);
              if (value == null) {
                  // delete header
                  mMsgHeader = matcher.replaceAll("");
              } else {
                  // replace header
                  String newString = name + ": " + value + mLineDelimiter;
                  mMsgHeader = matcher.replaceAll(Matcher.quoteReplacement(newString));
              }
  
              // set into hashtable
              replaceInternalHeaderFields(name, value);
          }
      }