code: public void setCustomHeader(String[] header) {
          if (header == null) {
              throw new IllegalArgumentException("Custom header can't be null.");
          }
          customHeader = new CustomHeaderLine[header.length];
          for (int i = 0; i < header.length; i++) {
              customHeader[i] = new CustomHeaderLine(header[i]);
          }
      }
docs: sets new customer header format specification
  
  @param header array of Strings containing optional parameters with name of the header value to
  use in them. For example: <Q>Java version: {java.version}</Q>.