fix: allow nullable service registrations of sub-dependencies

Author: wessberg

src/di-container.ts

@@ -213,7 +213,7 @@ export class DIContainer implements IDIContainer {
 					parentChain: nextParentChain
 				});
 
-				if (constructedInstance == null) {
+				if (constructedInstance == null && !this.has({identifier: dep})) {
 					throw new InstantiationError(`Dependency '${dep}' was not found in the service registry.`, {identifier: me.identifier, parentChain: nextParentChain});
 				}
 

test/di-container.test.ts

@@ -187,3 +187,26 @@ test(`Services that allow for nullable values can be constructed without excepti
 	container.registerSingleton<NullableServiceA>(() => undefined, {identifier: "NullableServiceA"});
 	assert.doesNotThrow(() => container.get<NullableServiceA>({identifier: "NullableServiceA"}));
 });
+
+test(`Services that allow for nullable values can be constructed without exceptions. #2`, () => {
+	interface IServiceA {
+		foo: string;
+	}
+
+	type NullableServiceA = IServiceA | undefined;
+
+	class ServiceB {
+		static get [CONSTRUCTOR_ARGUMENTS_SYMBOL]() {
+			return ["NullableServiceA"];
+		}
+
+		constructor(public serviceA: NullableServiceA) {}
+	}
+
+	const container = new DIContainer();
+
+	container.registerSingleton<NullableServiceA>(() => undefined, {identifier: "NullableServiceA"});
+	container.registerSingleton<ServiceB>(undefined, {identifier: "ServiceB", implementation: ServiceB});
+
+	assert.doesNotThrow(() => container.get<ServiceB>({identifier: "ServiceB"}));
+});