def add_error(e, span = nil)
      # Return if we've already logged this exception and it
      # is just propogating up the spans.
      return if e && e.instance_variable_get(:@instana_logged) || @current_span.nil?
      span ||= @current_span
      span.add_error(e)
    end
def add_error(e, span = nil)
      # Return if we've already logged this exception and it
      # is just propogating up the spans.
      return if e && e.instance_variable_get(:@instana_logged) || @current_span.nil?
      span ||= @current_span
      span.add_error(e)
    end
Log an error into the current span

 @param e [Exception] Add exception to the current span