code: @SuppressWarnings("unchecked")
      @CheckForNull
      protected PUB getPublicKey() {
          KeyPair keyPair = getKeyPair();
          return keyPair == null ? null : (PUB) keyPair.getPublic();
      }
docs: Shortcut to {@link KeyPair#getPublic()}.
  
  @return the public key. {@code null} if {@link #getKeyPair()} is {@code null}.