Could simply be

foreach ((array) get_class_methods($className) as $definedMethodName) {

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I think code should be as explicit as possible. Here we want to iterate methods if there are any. We don't want to cast the result to an array and iterate that and be depended on the result of the cast. To me it makes no sense that (array) null result in an empty array, I would expect an error. Another side effect of always casting is that it would be done even when not needed.

Casting to an array is something commonly used in the Symfony codebase, even in more critical paths where micro optimizations would matter more. To me the intention is clear, but I hear your arguments.

Also the issue here is more about class@anonymous not being a class name, which is why get_class_methods returns null as a way to notify there is an issue with the function call, not as I first thought a PHP inconsistency due to an anonymous class without any method. You don't access the generated internal class name here nor the instance, so it's expected to get null.

Agreed, micro optimizations are not needed here as it is already in error/exception path so fast execution is not that important.

Yes, sadly we cannot access the instance of the anonymous class here to figure out what methods are on there, so I guess this is the best we can do.

Let me know if the array cast is a deal breaker for the PR to be merged, always happy to agree to disagree and update a PR if the end-result is better than the current state :)

looking at the comments below, this could be turned to: if (!class_exists($className, false)), isn'it?

That would decrease the number of failures indeed.
However the docs of get_class_methods state it will return null on error, not that it will only return null when passing a "class name" of an anonymous class. Checking the return value of get-class-methods for null seems to me the safe bet.

do we know any other condition that could make this return null? if not, it'd be more readable to use class_exists, don't you thing?

I didn't check the implementation of get_class_methods, however the API docs. leave it open on when an error can happen. I've update the code in a way we've the best of the two solutions, i.e. we do the class_exists check first but still check the result of get_class_methods. This way the code will keep working even if get_class_methods might return null later on because of changes in the implementation. Let me know what you think!