[Bug]: Filter might cause Exceptions when they are not set

[AlternateIf]

Expected behavior

When a filter is not set, no condition is added and no exception/warning is produced

Actual behavior

In case of a filter being EMPTY_STRING or unset the current implementation leads to an exception since trim expects its argument to be a string but gets null

See https://github.com/pimcore/ecommerce-framework-bundle/blob/1.x/src/FilterService/FilterType/ElasticSearch/SelectFromMultiSelect.php#L35 for example

Maybe cast it to string like it was done here
https://github.com/pimcore/ecommerce-framework-bundle/blob/1.x/src/FilterService/FilterType/ElasticSearch/Select.php#L44
or do the trim only when it the value is not null like it was done here: https://github.com/pimcore/ecommerce-framework-bundle/blob/1.x/src/FilterService/FilterType/ElasticSearch/SelectCategory.php#L79

This also applies to the non Elastic Search Equivalent of SelectFromMultiSelect and the Input filter

Steps to reproduce

[github-actions]

Thanks a lot for reporting the issue. We did not consider the issue as "Pimcore:Priority", "Pimcore:ToDo" or "Pimcore:Backlog", so we're not going to work on that anytime soon. Please create a pull request to fix the issue if this is a bug report. We'll then review it as quickly as possible. If you're interested in contributing a feature, please contact us first here before creating a pull request. We'll then decide whether we'd accept it or not. Thanks for your understanding.