If I remove the check, this test would fail:

https://github.com/rails/rails/blob/master/activerecord/test/cases/scoping/default_scoping_test.rb#L169

With this error:

````
DefaultScopingTest#test_unscope_select:
NoMethodError: undefined method `map' for "Jamis":String
    /vagrant/rails/activerecord/lib/active_record/relation/query_methods.rb:233:in `block (2 levels) in select!'
    /vagrant/rails/activerecord/lib/active_record/relation/query_methods.rb:232:in `each'
    /vagrant/rails/activerecord/lib/active_record/relation/query_methods.rb:232:in `map'
    /vagrant/rails/activerecord/lib/active_record/relation/query_methods.rb:232:in `block in select!'
    /vagrant/rails/activerecord/lib/active_record/relation/query_methods.rb:230:in `each_index'
    /vagrant/rails/activerecord/lib/active_record/relation/query_methods.rb:230:in `select!'
    /vagrant/rails/activerecord/lib/active_record/relation/query_methods.rb:225:in `select'
    test/cases/scoping/default_scoping_test.rb:169:in `test_unscope_select'
````

Although, perhaps the check should be verifying that we have an Array, instead that it is not a String. I will change that too.