Bug fix for issue #14696, things changed are;

- Empty class type will now throw an error,
- Trailing comma in class type will also throw an error,
- Added tests for empty class type parameter,
- Updated tests for class type parameters with trailing comma

This behavior is consistently following function or method like when its type parameter is either empty or has trailing comma.

src/compiler/checker.ts

@@ -19559,7 +19559,7 @@ namespace ts {
         }
 
         function checkClassLikeDeclaration(node: ClassLikeDeclaration) {
-            checkGrammarClassDeclarationHeritageClauses(node);
+            checkGrammarClassLikeDeclaration(node);
             checkDecorators(node);
             if (node.name) {
                 checkTypeNameIsReserved(node.name, Diagnostics.Class_name_cannot_be_0);
@@ -22520,6 +22520,11 @@ namespace ts {
                 checkGrammarParameterList(node.parameters) || checkGrammarArrowFunction(node, file);
         }
 
+        function checkGrammarClassLikeDeclaration(node: ClassLikeDeclaration): boolean {
+            const file = getSourceFileOfNode(node);
+            return checkGrammarClassDeclarationHeritageClauses(node) || checkGrammarTypeParameterList(node.typeParameters, file);
+        }
+
         function checkGrammarArrowFunction(node: FunctionLikeDeclaration, file: SourceFile): boolean {
             if (node.kind === SyntaxKind.ArrowFunction) {
                 const arrowFunction = <ArrowFunction>node;

tests/baselines/reference/classWithEmptyTypeParameter.errors.txt

@@ -0,0 +1,8 @@
+tests/cases/compiler/classWithEmptyTypeParameter.ts(1,8): error TS1098: Type parameter list cannot be empty.
+
+
+==== tests/cases/compiler/classWithEmptyTypeParameter.ts (1 errors) ====
+    class C<> {
+           ~~
+!!! error TS1098: Type parameter list cannot be empty.
+    }

tests/baselines/reference/classWithEmptyTypeParameter.js

@@ -0,0 +1,10 @@
+//// [classWithEmptyTypeParameter.ts]
+class C<> {
+}
+
+//// [classWithEmptyTypeParameter.js]
+var C = (function () {
+    function C() {
+    }
+    return C;
+}());

tests/baselines/reference/typeParameterListWithTrailingComma1.errors.txt

@@ -0,0 +1,8 @@
+tests/cases/compiler/typeParameterListWithTrailingComma1.ts(1,10): error TS1009: Trailing comma not allowed.
+
+
+==== tests/cases/compiler/typeParameterListWithTrailingComma1.ts (1 errors) ====
+    class C<T,> {
+             ~
+!!! error TS1009: Trailing comma not allowed.
+    }

tests/cases/compiler/classWithEmptyTypeParameter.ts

@@ -0,0 +1,2 @@
+class C<> {
+}