Micro optimizations in type combinator.

Author: mad-briller

src/Type/TypeCombinator.php

@@ -40,8 +40,10 @@ class TypeCombinator
 
 	public static function addNull(Type $type): Type
 	{
-		if ((new NullType())->isSuperTypeOf($type)->no()) {
-			return self::union($type, new NullType());
+		$nullType = new NullType();
+
+		if ($nullType->isSuperTypeOf($type)->no()) {
+			return self::union($type, $nullType);
 		}
 
 		return $type;
@@ -241,8 +243,12 @@ public static function union(Type ...$types): Type
 
 		// simplify string[] | int[] to (string|int)[]
 		for ($i = 0; $i < $typesCount; $i++) {
+			if (! $types[$i] instanceof IterableType) {
+				continue;
+			}
+
 			for ($j = $i + 1; $j < $typesCount; $j++) {
-				if ($types[$i] instanceof IterableType && $types[$j] instanceof IterableType) {
+				if ($types[$j] instanceof IterableType) {
 					$types[$i] = new IterableType(
 						self::union($types[$i]->getIterableKeyType(), $types[$j]->getIterableKeyType()),
 						self::union($types[$i]->getIterableValueType(), $types[$j]->getIterableValueType()),