Handle undefined location.parent when getting completionEntryDetails (microsoft#54138)

Author: MariaSolOs

src/services/symbolDisplay.ts

@@ -452,7 +452,7 @@ export function getSymbolDisplayPartsDocumentationAndSymbolKind(typeChecker: Typ
         displayParts.push(spacePart());
         displayParts.push(operatorPart(SyntaxKind.EqualsToken));
         displayParts.push(spacePart());
-        addRange(displayParts, typeToDisplayParts(typeChecker, isConstTypeReference(location.parent) ? typeChecker.getTypeAtLocation(location.parent) : typeChecker.getDeclaredTypeOfSymbol(symbol), enclosingDeclaration, TypeFormatFlags.InTypeAlias));
+        addRange(displayParts, typeToDisplayParts(typeChecker, location.parent && isConstTypeReference(location.parent) ? typeChecker.getTypeAtLocation(location.parent) : typeChecker.getDeclaredTypeOfSymbol(symbol), enclosingDeclaration, TypeFormatFlags.InTypeAlias));
     }
     if (symbolFlags & SymbolFlags.Enum) {
         prefixNextMeaning();