code: @Nonnull
      LessException createException( Throwable cause ) {
          LessException lessEx = cause.getClass() == LessException.class ? (LessException)cause : new LessException( cause );
          lessEx.addPosition( filename, line, column );
          return lessEx;
      }
docs: If cause is already a LessException then filename, line number and column of the current object are added to the less stacktrace.
  With any other type of exception a new LessException is created.
  @param cause the cause
  @return the exception