def hash_value(key)
      if :hash == self.type
        value_node = self.children.find { |pair_node| pair_node.key.to_value == key }
        value_node ? value_node.value : nil
      else
        raise Synvert::Core::MethodNotSupported.new "has_key? is not handled for #{self.debug_info}"
      end
    end
def hash_value(key)
      if :hash == self.type
        value_node = self.children.find { |pair_node| pair_node.key.to_value == key }
        value_node ? value_node.value : nil
      else
        raise Synvert::Core::MethodNotSupported.new "has_key? is not handled for #{self.debug_info}"
      end
    end
Get hash value node according to specified key.

 @param [Object] key value.
 @return [Parser::AST::Node] value node.
 @raise [Synvert::Core::MethodNotSupported] if calls on other node.