diff --git a/src/tsconfig.strictNullChecks.json b/src/tsconfig.strictNullChecks.json
index ce1825fd1fb..536810fdfc9 100644
--- a/src/tsconfig.strictNullChecks.json
+++ b/src/tsconfig.strictNullChecks.json
@@ -72,6 +72,7 @@
 		"./vs/base/parts/contextmenu/electron-browser/contextmenu.ts",
 		"./vs/base/parts/contextmenu/electron-main/contextmenu.ts",
 		"./vs/base/parts/ipc/node/ipc.cp.ts",
+		"./vs/base/parts/ipc/node/ipc.net.ts",
 		"./vs/base/parts/ipc/node/ipc.ts",
 		"./vs/base/parts/ipc/test/node/testApp.ts",
 		"./vs/base/parts/ipc/test/node/testService.ts",
@@ -405,6 +406,7 @@
 		"./vs/platform/log/common/bufferLog.ts",
 		"./vs/platform/log/common/log.ts",
 		"./vs/platform/log/node/spdlogService.ts",
+		"./vs/platform/markers/common/markerService.ts",
 		"./vs/platform/markers/common/markers.ts",
 		"./vs/platform/menubar/common/menubar.ts",
 		"./vs/platform/node/minimalTranslations.ts",
@@ -489,6 +491,7 @@
 		"./vs/workbench/parts/logs/common/logConstants.ts",
 		"./vs/workbench/parts/markers/electron-browser/constants.ts",
 		"./vs/workbench/parts/markers/electron-browser/markers.ts",
+		"./vs/workbench/parts/markers/electron-browser/markersFileDecorations.ts",
 		"./vs/workbench/parts/markers/electron-browser/markersFilterOptions.ts",
 		"./vs/workbench/parts/markers/electron-browser/markersModel.ts",
 		"./vs/workbench/parts/markers/electron-browser/messages.ts",
diff --git a/src/vs/base/parts/ipc/node/ipc.net.ts b/src/vs/base/parts/ipc/node/ipc.net.ts
index 8a3d10a51c3..675e155162c 100644
--- a/src/vs/base/parts/ipc/node/ipc.net.ts
+++ b/src/vs/base/parts/ipc/node/ipc.net.ts
@@ -215,14 +215,19 @@ export class Server extends IPCServer {
 		}));
 	}
 
-	constructor(private server: NetServer) {
+	private server: NetServer | null;
+
+	constructor(server: NetServer) {
 		super(Server.toClientConnectionEvent(server));
+		this.server = server;
 	}
 
 	dispose(): void {
 		super.dispose();
-		this.server.close();
-		this.server = null;
+		if (this.server) {
+			this.server.close();
+			this.server = null;
+		}
 	}
 }
 
diff --git a/src/vs/platform/markers/common/markerService.ts b/src/vs/platform/markers/common/markerService.ts
index 0453c12fde7..a3fd07f7719 100644
--- a/src/vs/platform/markers/common/markerService.ts
+++ b/src/vs/platform/markers/common/markerService.ts
@@ -50,7 +50,7 @@ class MarkerStats implements MarkerStatistics {
 	warnings: number = 0;
 	unknowns: number = 0;
 
-	private _data: { [resource: string]: MarkerStatistics } = Object.create(null);
+	private _data?: { [resource: string]: MarkerStatistics } = Object.create(null);
 	private _service: IMarkerService;
 	private _subscription: IDisposable;
 
@@ -65,6 +65,10 @@ class MarkerStats implements MarkerStatistics {
 	}
 
 	private _update(resources: URI[]): void {
+		if (!this._data) {
+			return;
+		}
+
 		for (const resource of resources) {
 			const key = resource.toString();
 			const oldStats = this._data[key];
@@ -191,7 +195,6 @@ export class MarkerService implements IMarkerService {
 		}
 
 		// santize data
-		code = code || null;
 		startLineNumber = startLineNumber > 0 ? startLineNumber : 1;
 		startColumn = startColumn > 0 ? startColumn : 1;
 		endLineNumber = endLineNumber >= startLineNumber ? endLineNumber : startLineNumber;
@@ -200,7 +203,7 @@ export class MarkerService implements IMarkerService {
 		return {
 			resource,
 			owner,
-			code,
+			code: code || undefined,
 			severity,
 			message,
 			source,
@@ -221,13 +224,16 @@ export class MarkerService implements IMarkerService {
 		if (map) {
 			delete this._byOwner[owner];
 			for (const resource in map) {
-				// remeber what we remove
-				const [first] = MapMap.get(this._byResource, resource, owner);
-				if (first) {
-					changes.push(first.resource);
+				const entry = MapMap.get(this._byResource, resource, owner);
+				if (entry) {
+					// remeber what we remove
+					const [first] = entry;
+					if (first) {
+						changes.push(first.resource);
+					}
+					// actual remove
+					MapMap.remove(this._byResource, resource, owner);
 				}
-				// actual remove
-				MapMap.remove(this._byResource, resource, owner);
 			}
 		}
 
@@ -308,9 +314,9 @@ export class MarkerService implements IMarkerService {
 
 		} else {
 			// of one resource OR owner
-			const map: { [key: string]: IMarker[] } = owner
+			const map: { [key: string]: IMarker[] } | undefined = owner
 				? this._byOwner[owner]
-				: this._byResource[resource.toString()];
+				: resource ? this._byResource[resource.toString()] : undefined;
 
 			if (!map) {
 				return [];
diff --git a/src/vs/workbench/parts/markers/electron-browser/markersFileDecorations.ts b/src/vs/workbench/parts/markers/electron-browser/markersFileDecorations.ts
index 62d121cab32..13b739e57b7 100644
--- a/src/vs/workbench/parts/markers/electron-browser/markersFileDecorations.ts
+++ b/src/vs/workbench/parts/markers/electron-browser/markersFileDecorations.ts
@@ -27,12 +27,12 @@ class MarkersDecorationsProvider implements IDecorationsProvider {
 		this.onDidChange = _markerService.onMarkerChanged;
 	}
 
-	provideDecorations(resource: URI): IDecorationData {
+	provideDecorations(resource: URI): IDecorationData | undefined {
 		let markers = this._markerService.read({
 			resource,
 			severities: MarkerSeverity.Error | MarkerSeverity.Warning
 		});
-		let first: IMarker;
+		let first: IMarker | undefined;
 		for (const marker of markers) {
 			if (!first || marker.severity > first.severity) {
 				first = marker;
diff --git a/src/vs/workbench/services/decorations/browser/decorations.ts b/src/vs/workbench/services/decorations/browser/decorations.ts
index 5a24b725c08..ff98b24c992 100644
--- a/src/vs/workbench/services/decorations/browser/decorations.ts
+++ b/src/vs/workbench/services/decorations/browser/decorations.ts
@@ -31,7 +31,7 @@ export interface IDecoration {
 export interface IDecorationsProvider {
 	readonly label: string;
 	readonly onDidChange: Event<URI[]>;
-	provideDecorations(uri: URI, token: CancellationToken): IDecorationData | Thenable<IDecorationData>;
+	provideDecorations(uri: URI, token: CancellationToken): IDecorationData | Thenable<IDecorationData> | undefined;
 }
 
 export interface IResourceDecorationChangeEvent {