Ensure static variables are initialized (#10)

Author: frankdekker

src/Entity/Pair.php

@@ -79,7 +79,7 @@ public static function create(mixed $first, mixed $second): Pair
      */
     public static function empty(): Pair
     {
-        static $pair;
+        static $pair = null;
         $pair ??= new Pair(null, null);
 
         return $pair;

src/Entity/Side.php

@@ -69,14 +69,14 @@ public function select(mixed $left, mixed $right): mixed
 
     private static function left(): Side
     {
-        static $left;
+        static $left = null;
 
         return $left ??= new Side(self::LEFT);
     }
 
     private static function right(): Side
     {
-        static $right;
+        static $right = null;
 
         return $right ??= new Side(self::RIGHT);
     }

src/Util/Character.php

@@ -67,15 +67,14 @@ public static function isContinuousScript(int $codePoint): bool
             return false;
         }
 
-        static $table;
+        static $table = null;
         $table ??= require dirname(__DIR__, 2) . '/resources/NonContinuousScriptLookupTable.php';
 
         return $table[$codePoint] ?? true;
     }
 
     public static function isWhiteSpace(string $char): bool
     {
-        // TODO optimize function call. Replace calls with const
         return self::IS_WHITESPACE[$char] ?? false;
     }