framework/db/QueryTrait.php
protected function isEmpty($value)
    {
        return $value === '' || $value === [] || $value === null || is_string($value) && trim($value) === '';
    }
protected function isEmpty($value)
    {
        return $value === '' || $value === [] || $value === null || is_string($value) && trim($value) === '';
    }
Returns a value indicating whether the give value is "empty".

The value is considered "empty", if one of the following conditions is satisfied:

- it is `null`,
- an empty string (`''`),
- a string containing only whitespace characters,
- or an empty array.

@param mixed $value
@return bool if the value is empty