Exception not being caught; System.FinalException: Cannot modify a collection while it is being iterated

Question

Why is this Exception not being caught?

I read that System.LimitException is not caught but didn't see anywhere about System.FinalException.

Non-Working Code

@AuraEnabled
public static List<RecordType> getRecordTypes() {

    try {

        String sObjectType = 'Task';

        List<RecordType> recordTypes = RecordTypeRepository.getBySObjectType(sObjectType);

        return removeGenericTaskRecordType(recordTypes);

    } catch (Exception e) {

        String message = ErrorMessage.formatExceptionMessage(e, 'There was an error running NewTaskFormController getRecordTypes.');
        System.debug(message);
        throw new AuraHandledException(message);
    }
}


public static List<RecordType> removeGenericTaskRecordType(List<RecordType> recordTypes) {

    RecordType genericTask = RecordTypeRepository.getById(RecordTypeRepository.GENERIC_TASK_ID);

    Integer genericTaskIndex = recordTypes.indexOf(genericTask);

    for (RecordType recordType: recordTypes) {
        recordTypes.remove(genericTaskIndex );
    }


    return recordTypes;
}

What I've Tried

• The same code structure (try-catch) just a different exception and it does get caught. "common.apex.runtime.impl.ExecutionException: List index out of bounds: -1

Working-Code Example

 public static List<RecordType> removeGenericTaskRecordType(List<RecordType> recordTypes) {

    RecordType genericTask = RecordTypeRepository.getById(RecordTypeRepository.GENERIC_TASK_ID);

    Integer genericTaskIndex = -1;

    recordTypes.remove(genericTaskIndex);

    return recordTypes;
}

Answer 1

Your exception is not being caught because FinalException is not catchable. Neither are LimitException nor AssertException.

You can quickly check for yourself if a given type of exception is catchable using an anonymous script like the following:

try
{
    throw new FinalException();
}
catch (Exception pokemon)
{
    system.debug('Cannot catch em all');
}

Note that in general:

• you should know what specific types of exception you are expecting and catch only those
• it is better to avoid the exception entirely if it is preventable, even if it can be caught

Answer 2

Answer from @Adrian is good, but on a different note the reason why you're getting this error was because your code attempts to modify a collection while it is being iterated in the for each loop, which is not allowed. Read about Read-only Collections

If you need to modify the List or Set while iterating over it, use a simple for loop with a counter instead of the Set or List iteration.

for (Integer i = accts.size()-1;  i>=0 ; i--) {
    Account a = accts[i];
}