The property Cake\Http\ServerRequest::$data has been deprecated with message: 3.4.0 This public property will be removed in 4.0.0. Use getData() instead.
This property has been deprecated. The supplier of the class has supplied an explanatory message.
The explanatory message should give you some clue as to whether and when the property will be
removed from the class and what other property to use instead.
In PHP it is possible to write to properties without declaring them. For example, the following is perfectly valid PHP code:
Generally, it is a good practice to explictly declare properties to avoid accidental typos and provide IDE auto-completion: