diff --git a/src/vs/editor/contrib/gotoError/gotoErrorWidget.ts b/src/vs/editor/contrib/gotoError/gotoErrorWidget.ts
index 89f2f75d243..9da6b13042f 100644
--- a/src/vs/editor/contrib/gotoError/gotoErrorWidget.ts
+++ b/src/vs/editor/contrib/gotoError/gotoErrorWidget.ts
@@ -228,7 +228,7 @@ export class MarkerNavigationWidget extends PeekViewWidget {
 
 	protected _fillHead(container: HTMLElement): void {
 		super._fillHead(container);
-		this._actionbarWidget.push(this.actions, { label: false, icon: true });
+		this._actionbarWidget!.push(this.actions, { label: false, icon: true });
 	}
 
 	protected _fillTitleIcon(container: HTMLElement): void {
diff --git a/src/vs/editor/contrib/referenceSearch/peekViewWidget.ts b/src/vs/editor/contrib/referenceSearch/peekViewWidget.ts
index c40368e0311..4dd63cadd03 100644
--- a/src/vs/editor/contrib/referenceSearch/peekViewWidget.ts
+++ b/src/vs/editor/contrib/referenceSearch/peekViewWidget.ts
@@ -84,12 +84,12 @@ export abstract class PeekViewWidget extends ZoneWidget {
 
 	private _onDidClose = new Emitter<PeekViewWidget>();
 
-	protected _headElement: HTMLDivElement;
-	protected _primaryHeading: HTMLElement;
-	protected _secondaryHeading: HTMLElement;
-	protected _metaHeading: HTMLElement;
-	protected _actionbarWidget: ActionBar;
-	protected _bodyElement: HTMLDivElement;
+	protected _headElement?: HTMLDivElement;
+	protected _primaryHeading?: HTMLElement;
+	protected _secondaryHeading?: HTMLElement;
+	protected _metaHeading?: HTMLElement;
+	protected _actionbarWidget?: ActionBar;
+	protected _bodyElement?: HTMLDivElement;
 
 	constructor(editor: ICodeEditor, options: IPeekViewOptions = {}) {
 		super(editor, options);
@@ -139,8 +139,8 @@ export abstract class PeekViewWidget extends ZoneWidget {
 	protected _fillContainer(container: HTMLElement): void {
 		this.setCssClass('peekview-widget');
 
-		this._headElement = dom.$('.head');
-		this._bodyElement = dom.$('.body');
+		this._headElement = dom.$<HTMLDivElement>('.head');
+		this._bodyElement = dom.$<HTMLDivElement>('.body');
 
 		this._fillHead(this._headElement);
 		this._fillBody(this._bodyElement);
@@ -151,7 +151,7 @@ export abstract class PeekViewWidget extends ZoneWidget {
 
 	protected _fillHead(container: HTMLElement): void {
 		const titleElement = dom.$('.peekview-title');
-		dom.append(this._headElement, titleElement);
+		dom.append(this._headElement!, titleElement);
 		dom.addStandardDisposableListener(titleElement, 'click', event => this._onTitleClick(event));
 
 		this._fillTitleIcon(titleElement);
@@ -161,7 +161,7 @@ export abstract class PeekViewWidget extends ZoneWidget {
 		dom.append(titleElement, this._primaryHeading, this._secondaryHeading, this._metaHeading);
 
 		const actionsContainer = dom.$('.peekview-actions');
-		dom.append(this._headElement, actionsContainer);
+		dom.append(this._headElement!, actionsContainer);
 
 		const actionBarOptions = this._getActionBarOptions();
 		this._actionbarWidget = new ActionBar(actionsContainer, actionBarOptions);
@@ -185,20 +185,24 @@ export abstract class PeekViewWidget extends ZoneWidget {
 	}
 
 	public setTitle(primaryHeading: string, secondaryHeading?: string): void {
-		this._primaryHeading.innerHTML = strings.escape(primaryHeading);
-		this._primaryHeading.setAttribute('aria-label', primaryHeading);
-		if (secondaryHeading) {
-			this._secondaryHeading.innerHTML = strings.escape(secondaryHeading);
-		} else {
-			dom.clearNode(this._secondaryHeading);
+		if (this._primaryHeading && this._secondaryHeading) {
+			this._primaryHeading.innerHTML = strings.escape(primaryHeading);
+			this._primaryHeading.setAttribute('aria-label', primaryHeading);
+			if (secondaryHeading) {
+				this._secondaryHeading.innerHTML = strings.escape(secondaryHeading);
+			} else {
+				dom.clearNode(this._secondaryHeading);
+			}
 		}
 	}
 
 	public setMetaTitle(value: string): void {
-		if (value) {
-			this._metaHeading.innerHTML = strings.escape(value);
-		} else {
-			dom.clearNode(this._metaHeading);
+		if (this._metaHeading) {
+			if (value) {
+				this._metaHeading.innerHTML = strings.escape(value);
+			} else {
+				dom.clearNode(this._metaHeading);
+			}
 		}
 	}
 
@@ -220,11 +224,15 @@ export abstract class PeekViewWidget extends ZoneWidget {
 	}
 
 	protected _doLayoutHead(heightInPixel: number, widthInPixel: number): void {
-		this._headElement.style.height = `${heightInPixel}px`;
-		this._headElement.style.lineHeight = this._headElement.style.height;
+		if (this._headElement) {
+			this._headElement.style.height = `${heightInPixel}px`;
+			this._headElement.style.lineHeight = this._headElement.style.height;
+		}
 	}
 
 	protected _doLayoutBody(heightInPixel: number, widthInPixel: number): void {
-		this._bodyElement.style.height = `${heightInPixel}px`;
+		if (this._bodyElement) {
+			this._bodyElement.style.height = `${heightInPixel}px`;
+		}
 	}
 }
diff --git a/src/vs/platform/progress/common/progress.ts b/src/vs/platform/progress/common/progress.ts
index 117e1af70de..4308c72ce89 100644
--- a/src/vs/platform/progress/common/progress.ts
+++ b/src/vs/platform/progress/common/progress.ts
@@ -90,13 +90,13 @@ export interface IProgress<T> {
 export class Progress<T> implements IProgress<T> {
 
 	private _callback: (data: T) => void;
-	private _value: T;
+	private _value?: T;
 
 	constructor(callback: (data: T) => void) {
 		this._callback = callback;
 	}
 
-	get value() {
+	get value(): T | undefined {
 		return this._value;
 	}
 
diff --git a/src/vs/vscode.d.ts b/src/vs/vscode.d.ts
index 25271cbcf99..38ff2ab34d1 100644
--- a/src/vs/vscode.d.ts
+++ b/src/vs/vscode.d.ts
@@ -2786,7 +2786,7 @@ declare module 'vscode' {
 		 * *Note* that the eol-sequence will be applied to the
 		 * whole document.
 		 */
-		newEol: EndOfLine;
+		newEol?: EndOfLine;
 
 		/**
 		 * Create a new TextEdit.
diff --git a/src/vs/workbench/api/common/extHostDocumentSaveParticipant.ts b/src/vs/workbench/api/common/extHostDocumentSaveParticipant.ts
index ae129051fe8..f55a89b3f30 100644
--- a/src/vs/workbench/api/common/extHostDocumentSaveParticipant.ts
+++ b/src/vs/workbench/api/common/extHostDocumentSaveParticipant.ts
@@ -153,7 +153,7 @@ export class ExtHostDocumentSaveParticipant implements ExtHostDocumentSavePartic
 						resourceEdit.edits.push({
 							range: range && Range.from(range),
 							text: newText,
-							eol: EndOfLine.from(newEol)
+							eol: newEol && EndOfLine.from(newEol)
 						});
 					}
 				}
diff --git a/src/vs/workbench/api/common/extHostTextEditor.ts b/src/vs/workbench/api/common/extHostTextEditor.ts
index fa10d30014b..1e5404bbf2b 100644
--- a/src/vs/workbench/api/common/extHostTextEditor.ts
+++ b/src/vs/workbench/api/common/extHostTextEditor.ts
@@ -151,11 +151,11 @@ export class ExtHostTextEditorOptions implements vscode.TextEditorOptions {
 	private _proxy: MainThreadTextEditorsShape;
 	private _id: string;
 
-	private _tabSize: number;
-	private _indentSize: number;
-	private _insertSpaces: boolean;
-	private _cursorStyle: TextEditorCursorStyle;
-	private _lineNumbers: TextEditorLineNumbersStyle;
+	private _tabSize!: number;
+	private _indentSize!: number;
+	private _insertSpaces!: boolean;
+	private _cursorStyle!: TextEditorCursorStyle;
+	private _lineNumbers!: TextEditorLineNumbersStyle;
 
 	constructor(proxy: MainThreadTextEditorsShape, id: string, source: IResolvedTextEditorConfiguration) {
 		this._proxy = proxy;
diff --git a/src/vs/workbench/api/common/extHostTypeConverters.ts b/src/vs/workbench/api/common/extHostTypeConverters.ts
index 5da072a265e..f7827afe487 100644
--- a/src/vs/workbench/api/common/extHostTypeConverters.ts
+++ b/src/vs/workbench/api/common/extHostTypeConverters.ts
@@ -442,7 +442,7 @@ export namespace TextEdit {
 	export function from(edit: vscode.TextEdit): modes.TextEdit {
 		return <modes.TextEdit>{
 			text: edit.newText,
-			eol: EndOfLine.from(edit.newEol),
+			eol: edit.newEol && EndOfLine.from(edit.newEol),
 			range: Range.from(edit.range)
 		};
 	}
diff --git a/src/vs/workbench/api/common/extHostTypes.ts b/src/vs/workbench/api/common/extHostTypes.ts
index 9ad1d38f66e..9b0cd9c9cc8 100644
--- a/src/vs/workbench/api/common/extHostTypes.ts
+++ b/src/vs/workbench/api/common/extHostTypes.ts
@@ -514,7 +514,7 @@ export class TextEdit {
 
 	protected _range: Range;
 	protected _newText: string | null;
-	protected _newEol: EndOfLine;
+	protected _newEol?: EndOfLine;
 
 	get range(): Range {
 		return this._range;
@@ -538,11 +538,11 @@ export class TextEdit {
 		this._newText = value;
 	}
 
-	get newEol(): EndOfLine {
+	get newEol(): EndOfLine | undefined {
 		return this._newEol;
 	}
 
-	set newEol(value: EndOfLine) {
+	set newEol(value: EndOfLine | undefined) {
 		if (value && typeof value !== 'number') {
 			throw illegalArgument('newEol');
 		}
@@ -550,7 +550,7 @@ export class TextEdit {
 	}
 
 	constructor(range: Range, newText: string | null) {
-		this.range = range;
+		this._range = range;
 		this._newText = newText;
 	}
 
@@ -798,7 +798,7 @@ export class Location {
 	}
 
 	uri: URI;
-	range: Range;
+	range!: Range;
 
 	constructor(uri: URI, rangeOrPosition: Range | Position) {
 		this.uri = uri;
@@ -861,10 +861,10 @@ export class Diagnostic {
 
 	range: Range;
 	message: string;
-	source: string;
-	code: string | number;
 	severity: DiagnosticSeverity;
-	relatedInformation: DiagnosticRelatedInformation[];
+	source?: string;
+	code?: string | number;
+	relatedInformation?: DiagnosticRelatedInformation[];
 	tags?: DiagnosticTag[];
 
 	constructor(range: Range, message: string, severity: DiagnosticSeverity = DiagnosticSeverity.Error) {
@@ -989,7 +989,7 @@ export class SymbolInformation {
 	}
 
 	name: string;
-	location: Location;
+	location!: Location;
 	kind: SymbolKind;
 	containerName: string | undefined;
 
@@ -1253,8 +1253,8 @@ export class SignatureInformation {
 export class SignatureHelp {
 
 	signatures: SignatureInformation[];
-	activeSignature: number;
-	activeParameter: number;
+	activeSignature: number = 0;
+	activeParameter: number = 0;
 
 	constructor() {
 		this.signatures = [];
@@ -1310,19 +1310,19 @@ export enum CompletionItemKind {
 export class CompletionItem implements vscode.CompletionItem {
 
 	label: string;
-	kind: CompletionItemKind | undefined;
+	kind?: CompletionItemKind;
 	detail?: string;
 	documentation?: string | MarkdownString;
 	sortText?: string;
 	filterText?: string;
 	preselect?: boolean;
-	insertText: string | SnippetString;
+	insertText?: string | SnippetString;
 	keepWhitespace?: boolean;
-	range: Range;
+	range?: Range;
 	commitCharacters?: string[];
-	textEdit: TextEdit;
-	additionalTextEdits: TextEdit[];
-	command: vscode.Command;
+	textEdit?: TextEdit;
+	additionalTextEdits?: TextEdit[];
+	command?: vscode.Command;
 
 	constructor(label: string, kind?: CompletionItemKind) {
 		this.label = label;
diff --git a/src/vs/workbench/contrib/callHierarchy/browser/callHierarchyPeek.ts b/src/vs/workbench/contrib/callHierarchy/browser/callHierarchyPeek.ts
index 3679e656809..1166da97f9c 100644
--- a/src/vs/workbench/contrib/callHierarchy/browser/callHierarchyPeek.ts
+++ b/src/vs/workbench/contrib/callHierarchy/browser/callHierarchyPeek.ts
@@ -386,7 +386,7 @@ export class CallHierarchyTreePeekWidget extends PeekViewWidget {
 			};
 			this._changeDirectionAction = new ChangeHierarchyDirectionAction(this._direction, changeDirection);
 			this._disposables.add(this._changeDirectionAction);
-			this._actionbarWidget.push(this._changeDirectionAction, { icon: true, label: false });
+			this._actionbarWidget!.push(this._changeDirectionAction, { icon: true, label: false });
 		}
 	}
 
diff --git a/src/vs/workbench/contrib/scm/browser/dirtydiffDecorator.ts b/src/vs/workbench/contrib/scm/browser/dirtydiffDecorator.ts
index 97539eb481f..955579069d7 100644
--- a/src/vs/workbench/contrib/scm/browser/dirtydiffDecorator.ts
+++ b/src/vs/workbench/contrib/scm/browser/dirtydiffDecorator.ts
@@ -234,7 +234,7 @@ class DirtyDiffWidget extends PeekViewWidget {
 		const changeTypeColor = getChangeTypeColor(this.themeService.getTheme(), changeType);
 		this.style({ frameColor: changeTypeColor, arrowColor: changeTypeColor });
 
-		this._actionbarWidget.context = [this.model.modified!.uri, this.model.changes, index];
+		this._actionbarWidget!.context = [this.model.modified!.uri, this.model.changes, index];
 		this.show(position, height);
 		this.editor.focus();
 	}
@@ -255,11 +255,11 @@ class DirtyDiffWidget extends PeekViewWidget {
 
 		this._disposables.add(previous);
 		this._disposables.add(next);
-		this._actionbarWidget.push([previous, next], { label: false, icon: true });
+		this._actionbarWidget!.push([previous, next], { label: false, icon: true });
 
 		const actions: IAction[] = [];
 		this._disposables.add(createAndFillInActionBarActions(this.menu, { shouldForwardArgs: true }, actions));
-		this._actionbarWidget.push(actions, { label: false, icon: true });
+		this._actionbarWidget!.push(actions, { label: false, icon: true });
 	}
 
 	protected _getActionBarOptions(): IActionBarOptions {