fix(frontend, v1.2): reject null payloads in dashboard type predicates

frontend/src/app/common/util/predicate.ts

@@ -25,3 +25,13 @@
 export function isDefined<T>(val: T | undefined | null): val is T {
   return val !== undefined && val != null;
 }
+
+/**
+ * checks that the given value is a non-null object in the `typeof` sense,
+ * guarding against the JavaScript quirk that `typeof null === "object"`.
+ * @param x
+ * @returns {boolean}
+ */
+export function isNonNullObject(x: unknown): x is object {
+  return typeof x === "object" && x !== null;
+}

frontend/src/app/dashboard/type/type-predicates.ts

@@ -22,23 +22,24 @@ import { DashboardProject } from "./dashboard-project.interface";
 import { DashboardFile } from "./dashboard-file.interface";
 import { DashboardDataset } from "./dashboard-dataset.interface";
 import { DashboardWorkflowComputingUnit } from "../../common/type/workflow-computing-unit";
+import { isNonNullObject } from "../../common/util/predicate";
 
 export function isDashboardWorkflow(value: any): value is DashboardWorkflow {
-  return value && typeof value.workflow === "object";
+  return !!value && isNonNullObject(value.workflow);
 }
 
 export function isDashboardProject(value: any): value is DashboardProject {
-  return value && typeof value.name === "string" && !value.workflow;
+  return !!value && typeof value.name === "string" && !value.workflow;
 }
 
 export function isDashboardFile(value: any): value is DashboardFile {
-  return value && typeof value.ownerEmail === "string" && typeof value.file === "object";
+  return !!value && typeof value.ownerEmail === "string" && isNonNullObject(value.file);
 }
 
 export function isDashboardDataset(value: any): value is DashboardDataset {
-  return value && typeof value.dataset === "object";
+  return !!value && isNonNullObject(value.dataset);
 }
 
 export function isDashboardWorkflowComputingUnit(value: any): value is DashboardWorkflowComputingUnit {
-  return value && typeof value.computingUnit === "object";
+  return !!value && isNonNullObject(value.computingUnit);
 }