Running data recurring… Warning: count(): Parameter must be an array or an object that implements Countable in lib/internal/Magento/Framework/View/Design/Theme/ThemeList.php on line 237
I have encountered this issue in a bin/magento setup:upgrade response after upgrading PHP to 7.2.
Calling count() on a scalar or object that doesn’t implement the Countable interface returns 1.
There are no known use cases for this, and it can easily hide bugs <…>.
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This RFC proposes adding a warning when calling count() with a parameter that is a scalar, null, or an object that doesn’t implement Countable.