code: public static Header header(Map<String, Object> header) {
          return Classes.newInstance("io.jsonwebtoken.impl.DefaultHeader", MAP_ARG, header);
      }
docs: Creates a new {@link Header} instance suitable for <em>plaintext</em> (not digitally signed) JWTs, populated
  with the specified name/value pairs.  As this is a less common use of JWTs, consider using the
  {@link #jwsHeader(java.util.Map)} factory method instead if you will later digitally sign the JWT.
  
  @return a new {@link Header} instance suitable for <em>plaintext</em> (not digitally signed) JWTs.