FIx for "empty" strings (#50335)

Avoid exception passed string is just spaces.
Example: str('   ')->apa() was failing.

Author: tiagof

src/Illuminate/Support/Str.php

@@ -1298,7 +1298,7 @@ public static function headline($value)
      */
     public static function apa($value)
     {
-        if ($value === '') {
+        if (trim($value) === '') {
             return $value;
         }