StripTags and Trim shouldn't fail if the argument is empty

We have faced similar issue in case if multivalued text field is getting empty array. In that case empty array is getting passed and exception is coming. Updated patch to avoid this case.

Reverting back to the check in patch #2 as this change forms part of the bigger #3332785 issue + adding tests.

Thanks for the patches - sorry its taken a year and a half to respond.

Automatically closed - issue fixed for 2 weeks with no activity.