Fixes `Deprecated: strtolower(): Passing null to string in libraries/…

…src/Log/Log.php on line 387` (joomla#37009)

Fixes `Deprecated: strtolower(): Passing null to parameter #1 ($string) of type string is deprecated in libraries/src/Log/Log.php on line 387`

libraries/src/Log/Log.php

@@ -384,7 +384,7 @@ protected function findLoggers($priority, $category)
 
 		// Sanitize inputs.
 		$priority = (int) $priority;
-		$category = strtolower($category);
+		$category = strtolower((string) $category);
 
 		// Let's go iterate over the loggers and get all the ones we need.
 		foreach ((array) $this->lookup as $signature => $rules)