# File lib_wpm/wpm.rb, line 1097
    def fetch_value(prop_name, prop_value, check_type=nil, not_allow_nil=false)
      case (prop_value)
      when Proc
        ret_val = prop_value.call
      else
        ret_val = prop_value
      end

      unless (not_allow_nil) then
        if (ret_val.nil?) then
          return nil
        end
      end

      if (check_type) then
        check_type(prop_name, ret_val, check_type)
      end

      ret_val
    end