[BUGFIX beta] Make container always return the same value even if the registered value is falsy

[hibariya]

This fixes #12796.

[rwjblue]

Looks good to me.

@dgeb / @stefanpenner - r?

[stefanpenner]

isn't this expression the opposite of what we want?

[hibariya]

I couldn't understand what is the problem. I think this change is necessary for the following case:

QUnit.test('The value returned from resolver is the same value as the original value even if the value is falsy', function() {
  let resolver = {
    resolve(fullName) {
      if (fullName === 'falsy:value') {
        return null;
      }
    }
  };
  let registry = new Registry({ resolver });

  deepEqual(registry.resolve('falsy:value'), null);
});

[hibariya]

I added the above test.

[dgeb]

Looks good to me as well. Thanks @hibariya 👍

[stefanpenner]

👍