Handle unresolved baseType when trying to get completions for static member

src/services/completions.ts

@@ -2012,7 +2012,9 @@ namespace ts.Completions {
                 // List of property symbols of base type that are not private and already implemented
                 const baseSymbols = flatMap(getAllSuperTypeNodes(decl), baseTypeNode => {
                     const type = typeChecker.getTypeAtLocation(baseTypeNode);
-                    return type && typeChecker.getPropertiesOfType(classElementModifierFlags & ModifierFlags.Static ? typeChecker.getTypeOfSymbolAtLocation(type.symbol, decl) : type);
+                    return classElementModifierFlags & ModifierFlags.Static ?
+                        type?.symbol && typeChecker.getPropertiesOfType(typeChecker.getTypeOfSymbolAtLocation(type.symbol, decl)) :
+                        type && typeChecker.getPropertiesOfType(type);
                 });
                 symbols = filterClassMembersList(baseSymbols, decl.members, classElementModifierFlags);
             }

tests/cases/fourslash/completionEntryForClassMembers_StaticWhenBaseTypeIsNotResolved.ts

@@ -0,0 +1,35 @@
+/// <reference path="fourslash.ts" />
+
+// @Filename: /node_modules/@types/react/index.d.ts
+//// export = React;
+//// export as namespace React;
+//// declare namespace React {
+////     function createElement(): any;
+////     interface Component<P = {}, S = {}, SS = any> { }
+////     class Component<P, S> {
+////         static contextType?: any;
+////         context: any;
+////         constructor(props: Readonly<P>);
+////         setState<K extends keyof S>(
+////             state: ((prevState: Readonly<S>, props: Readonly<P>) => (Pick<S, K> | S | null)) | (Pick<S, K> | S | null),
+////             callback?: () => void
+////         ): void;
+////     }
+//// }
+
+// @Filename: /a.ts
+//// import React from 'react'
+//// class Slider extends React.Component {
+////     static defau/**/ltProps = {
+////         onMouseDown: () => { },
+////         onMouseUp: () => { },
+////         unit: 'px',
+////     }
+////     handleChange = () => 10;
+//// }
+
+verify.completions({
+    marker: "",
+    isNewIdentifierLocation: true,
+    exact: completion.classElementKeywords,
+});