Add default parameter values to   method
Add default parameter values to   method

The \Concrete\Core\Controller\Controller::get method has a signature of get($identifier=null, $defaultValue=null). This signature was causing issues on PHP7.

Former-commit-id: 8174213182434f56dbd84b0180c69612422c6ade
Former-commit-id: 50dcf18f29b4ad587af4128c8966913f498966db
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