Fix Psalm issues

Author: trowski

src/SqlConfig.php

@@ -54,7 +54,9 @@ protected static function parseConnectionString(string $connectionString, array
 
         $offset = 0;
         foreach ($matches as [$pair, $key, $value, $quote]) {
-            if ($quote) {
+            \assert($value !== null);
+
+            if ($quote !== null) {
                 $value = \stripslashes(\substr($value, 1, -1));
 
                 if ($value === '') {