The return type could not be reliably inferred; please add a @return annotation.
Our type inference engine in quite powerful, but sometimes the code does not
provide enough clues to go by. In these cases we request you to add a @return
annotation as described here.
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: