code: @NullSafe
    public static String getMessage(Throwable throwable) {
      return (throwable != null ? throwable.getMessage() : null);
    }
docs: Null-safe method returning the message of the given {@link Throwable} object.  If the {@link Throwable} object
  reference is {@literal null} then this method returns {@literal null}.
  
  @param throwable {@link Throwable} object who's message is returned.
  @return the message of the given {@link Throwable} object.
  @see java.lang.Throwable#getMessage()