Yes, you will see this error only when you have PHP 7.2. I am not sure about PHP 7.0 and PHP 7.1 as I have not tested them. I was also getting the same error after installing PHP 7.2. I am using CMS 'question2answer'. It seems that if the function count() return NULL, PHP core returns this error. I did the following change in qa-include/app/format.php (line 384) of 'question2answer' to fix the error.
if (@$favoritemap['category'] && count(@$favoritemap['category']))
So, I think the quick fix should be:
if (any_variable && count(any_variable))