code: @Override
      public Builder subject(String username) throws InvalidClaimException {
          if (username != null && !username.isEmpty()) {
  
              claims.put(Claims.SUBJECT, username);
          } else {
              String err = Tr.formatMessage(tc, "JWT_INVALID_CLAIM_VALUE_ERR", new Object[] { Claims.SUBJECT, username });
              throw new InvalidClaimException(err);
          }
          return this;
      }
docs: /*
  (non-Javadoc)
  
  @see com.ibm.ws.security.jwt.internal.Builder#subject(java.lang.String)