The expression $collects of type string|null is loosely compared to true; this is ambiguous if the string can be empty. You might want to explicitly use !== null instead.
In PHP, under loose comparison (like ==, or !=, or switch conditions),
values of different types might be equal.
For string values, the empty string '' is a special case, in particular
the following results might be unexpected:
''==false// true''==null// true'ab'==false// false'ab'==null// false// It is often better to use strict comparison''===false// false''===null// false
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: