fixed empty docblock

src/APIlite.php

@@ -272,8 +272,11 @@ class APIlite
 		return null;
 	}
 
-	private function parseReturnDoc(string $doc): string|null
+	private function parseReturnDoc(?string $doc): string|null
 	{
+		if (is_null($doc) || $doc === '') {
+			return null;
+		}
 		$lines = explode("\n", $doc);
 		foreach ($lines as $line) {
 			if (strpos($line, '@return') !== false) {