def _evaluate_condition(condition)
      case condition
      when Symbol then self.send(condition)
      when Proc then self.instance_eval(&condition)
      else
        raise ArgumentError,
              'Filter condtions need to be either a Symbol or a Proc'
      end
    end
def _evaluate_condition(condition)
      case condition
      when Symbol then self.send(condition)
      when Proc then self.instance_eval(&condition)
      else
        raise ArgumentError,
              'Filter condtions need to be either a Symbol or a Proc'
      end
    end
Evaluates a filter condition (:if or :unless)

 ==== Parameters
 condition<Symbol, Proc>:: The condition to evaluate.

 ==== Raises
 ArgumentError:: condition not a Symbol or Proc.

 ==== Returns
 Boolean:: True if the condition is met.

 ==== Alternatives
 If condition is a symbol, it will be send'ed. If it is a Proc it will be
 called directly with self as an argument.

 :api: private