def evaluate_handler(handler)
      case handler
      when Symbol
        target.method(handler)
      when Proc
        if handler.arity.zero?
          proc { instance_exec(&handler) }
        else
          proc { |_exception| instance_exec(_exception, &handler) }
        end
      end
    end
def evaluate_handler(handler)
      case handler
      when Symbol
        target.method(handler)
      when Proc
        if handler.arity.zero?
          proc { instance_exec(&handler) }
        else
          proc { |_exception| instance_exec(_exception, &handler) }
        end
      end
    end
Executes given handler

 @api private