fix(55500): Incorrect error reported when using class extends null and re-opening interface

src/compiler/checker.ts

@@ -44656,8 +44656,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     if (!checkTypeAssignableTo(typeWithThis, baseWithThis, /*errorNode*/ undefined)) {
                         issueMemberSpecificError(node, typeWithThis, baseWithThis, Diagnostics.Class_0_incorrectly_extends_base_class_1);
                     }
-                    else {
-                        // Report static side error only when instance type is assignable
+                    else if (staticBaseType !== nullWideningType) {
+                        // Report static side error only when instance type is assignable and base type is not null
                         checkTypeAssignableTo(staticType, getTypeWithoutSignatures(staticBaseType), node.name || node, Diagnostics.Class_static_side_0_incorrectly_extends_base_class_static_side_1);
                     }
                     if (baseConstructorType.flags & TypeFlags.TypeVariable) {

tests/baselines/reference/classExtendsNull2.errors.txt

@@ -1,15 +1,12 @@
-classExtendsNull2.ts(5,7): error TS2417: Class static side 'typeof C' incorrectly extends base class static side 'null'.
 classExtendsNull2.ts(7,5): error TS17005: A constructor cannot contain a 'super' call when its class extends 'null'.
 
 
-==== classExtendsNull2.ts (2 errors) ====
+==== classExtendsNull2.ts (1 errors) ====
     // https://github.com/microsoft/TypeScript/issues/55499
     
     interface Base {}
     
     class C extends null {
-          ~
-!!! error TS2417: Class static side 'typeof C' incorrectly extends base class static side 'null'.
       constructor() {
         super();
         ~~~~~~~