code: public JWTPayload setIssuer(String issuer) {
          this.issuer = issuer;
          this.put(PayloadConstants.ISSUER, issuer);
          return this;
      }
docs: Sets the issuer claim that identifies the principal that issued the JWT or {@code null} for
  none.
  
  <p>
  Overriding is only supported for the purpose of calling the super implementation and changing
  the return type, but nothing else.
  </p>