Ruby's enumerable `all?` method returns `true` if receiver is blank.

ruby-enum-all-memo.md

[].all? #=> true

• https://docs.ruby-lang.org/en/2.4.0/Enumerable.html#method-i-all-3F
• https://github.com/ruby/ruby/blob/48f5f5915b0c357b05a9dda2732470bf67ebd691/test/ruby/test_enum.rb#L288
• https://github.com/ruby/ruby/blob/640bcdf217f69d83e96483a59ae7f9af4d534f43/enum.c#L1174
• https://github.com/ruby/ruby/blob/91587f6b63df794db6b4b2ce8f94f78344044ff2/vm_eval.c#L1220
• https://github.com/ruby/ruby/blob/91587f6b63df794db6b4b2ce8f94f78344044ff2/vm_eval.c#L1195
• https://github.com/ruby/ruby/blob/91587f6b63df794db6b4b2ce8f94f78344044ff2/vm_eval.c#L1141