Rule's inspect method fails when the rule is created through a SQL array

[frostblooded]

Steps to reproduce

Define ability with a SQL array and call #inspect.

Example

CanCan::Rule.new(true, :read, Watermelon, ['visible=?', true], {}, {}).inspect

Expected behavior

The method displays the rule in a string format.

Actual behavior

There is an error:

 TypeError:
       no implicit conversion of nil into String
     # ./lib/cancan/rule.rb:37:in `+'
     # ./lib/cancan/rule.rb:37:in `inspect'
     ...

System configuration

Rails version:
5.1.7 (not relevant)
Ruby version:
2.4.6 (not relevant)
CanCanCan version
3.0.1

[coorasse]

fixed in 3.0.2