diff --git a/extensions/typescript-language-features/src/features/bufferSyncSupport.ts b/extensions/typescript-language-features/src/features/bufferSyncSupport.ts
index bcb4ea1b4fef1563c9d86e245acb9f20a2653afc..e47947cff2f2403d11cec99b4a77547524c5cc0f 100644
--- a/extensions/typescript-language-features/src/features/bufferSyncSupport.ts
+++ b/extensions/typescript-language-features/src/features/bufferSyncSupport.ts
@@ -7,6 +7,7 @@ import * as vscode from 'vscode';
 import * as Proto from '../protocol';
 import { ITypeScriptServiceClient } from '../typescriptService';
 import API from '../utils/api';
+import { coalease } from '../utils/arrays';
 import { Delayer } from '../utils/async';
 import { nulToken } from '../utils/cancellation';
 import { Disposable } from '../utils/dispose';
@@ -278,9 +279,7 @@ class GetErrRequest {
 	) {
 		const args: Proto.GeterrRequestArgs = {
 			delay: 0,
-			files: Array.from(files.entries)
-				.map(entry => client.normalizedPath(entry.resource))
-				.filter(x => !!x) as string[]
+			files: coalease(Array.from(files.entries).map(entry => client.normalizedPath(entry.resource)))
 		};
 
 		client.executeAsync('geterr', args, _token.token)
diff --git a/extensions/typescript-language-features/src/features/folding.ts b/extensions/typescript-language-features/src/features/folding.ts
index 963c4fbb9e061aebc3b2f3e0613ce0010e3a6f08..4d6710358162e98786ad008cc65721a0d5926bd1 100644
--- a/extensions/typescript-language-features/src/features/folding.ts
+++ b/extensions/typescript-language-features/src/features/folding.ts
@@ -7,6 +7,7 @@ import * as vscode from 'vscode';
 import * as Proto from '../protocol';
 import { ITypeScriptServiceClient } from '../typescriptService';
 import API from '../utils/api';
+import { coalease } from '../utils/arrays';
 import { VersionDependentRegistration } from '../utils/dependentRegistration';
 import * as typeConverters from '../utils/typeConverters';
 
@@ -33,9 +34,7 @@ class TypeScriptFoldingProvider implements vscode.FoldingRangeProvider {
 			return;
 		}
 
-		return response.body
-			.map(span => this.convertOutliningSpan(span, document))
-			.filter(foldingRange => !!foldingRange) as vscode.FoldingRange[];
+		return coalease(response.body.map(span => this.convertOutliningSpan(span, document)));
 	}
 
 	private convertOutliningSpan(
diff --git a/extensions/typescript-language-features/src/features/tsconfig.ts b/extensions/typescript-language-features/src/features/tsconfig.ts
index 2a47c0887bd474f2eed0e7e29df03a875d7b0c05..b71a608c927eadf62a2d96bb6973a939930624ce 100644
--- a/extensions/typescript-language-features/src/features/tsconfig.ts
+++ b/extensions/typescript-language-features/src/features/tsconfig.ts
@@ -4,9 +4,9 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as jsonc from 'jsonc-parser';
-import { dirname, join, basename } from 'path';
+import { basename, dirname, join } from 'path';
 import * as vscode from 'vscode';
-import { flatten } from '../utils/arrays';
+import { coalease, flatten } from '../utils/arrays';
 
 function mapChildren<R>(node: jsonc.Node | undefined, f: (x: jsonc.Node) => R): R[] {
 	return node && node.type === 'array' && node.children
@@ -25,11 +25,11 @@ class TsconfigLinkProvider implements vscode.DocumentLinkProvider {
 			return null;
 		}
 
-		return [
+		return coalease([
 			this.getExtendsLink(document, root),
 			...this.getFilesLinks(document, root),
 			...this.getReferencesLinks(document, root)
-		].filter(x => !!x) as vscode.DocumentLink[];
+		]);
 	}
 
 	private getExtendsLink(document: vscode.TextDocument, root: jsonc.Node): vscode.DocumentLink | undefined {
@@ -68,7 +68,7 @@ class TsconfigLinkProvider implements vscode.DocumentLinkProvider {
 				}
 
 				return new vscode.DocumentLink(this.getRange(document, pathNode),
-					basename(pathNode.value).match('.json$')
+					basename(pathNode.value).endsWith('.json')
 						? this.getFileTarget(document, pathNode)
 						: this.getFolderTarget(document, pathNode));
 			});
diff --git a/extensions/typescript-language-features/src/typeScriptServiceClientHost.ts b/extensions/typescript-language-features/src/typeScriptServiceClientHost.ts
index 7e0d159132c60fcb8a3ffad6ca96378c9e1838f9..dda7adb82e641ca16b690bd3500fd7d809fc7a48 100644
--- a/extensions/typescript-language-features/src/typeScriptServiceClientHost.ts
+++ b/extensions/typescript-language-features/src/typeScriptServiceClientHost.ts
@@ -23,7 +23,7 @@ import { PluginManager } from './utils/plugins';
 import * as typeConverters from './utils/typeConverters';
 import TypingsStatus, { AtaProgressReporter } from './utils/typingsStatus';
 import VersionStatus from './utils/versionStatus';
-import { flatten } from './utils/arrays';
+import { flatten, coalease } from './utils/arrays';
 
 // Style check diagnostics that can be reported as warnings
 const styleCheckDiagnostics = [
@@ -245,13 +245,13 @@ export default class TypeScriptServiceClientHost extends Disposable {
 		}
 		const relatedInformation = diagnostic.relatedInformation;
 		if (relatedInformation) {
-			converted.relatedInformation = relatedInformation.map((info: any) => {
-				let span = info.span;
+			converted.relatedInformation = coalease(relatedInformation.map((info: any) => {
+				const span = info.span;
 				if (!span) {
 					return undefined;
 				}
 				return new vscode.DiagnosticRelatedInformation(typeConverters.Location.fromTextSpan(this.client.toResource(span.file), span), info.message);
-			}).filter((x: any) => !!x) as vscode.DiagnosticRelatedInformation[];
+			}));
 		}
 		if (diagnostic.reportsUnnecessary) {
 			converted.tags = [vscode.DiagnosticTag.Unnecessary];
diff --git a/extensions/typescript-language-features/src/utils/arrays.ts b/extensions/typescript-language-features/src/utils/arrays.ts
index f9435fe9b200291edb4fe920f88fd0c41ac25555..7c8f2d56ff6b9e286f046f987f6955b8e29b7d83 100644
--- a/extensions/typescript-language-features/src/utils/arrays.ts
+++ b/extensions/typescript-language-features/src/utils/arrays.ts
@@ -19,6 +19,10 @@ export function equals<T>(
 	return a.every((x, i) => itemEquals(x, b[i]));
 }
 
-export function flatten<T>(arr: ReadonlyArray<T>[]): T[] {
-	return Array.prototype.concat.apply([], arr);
-}
\ No newline at end of file
+export function flatten<T>(array: ReadonlyArray<T>[]): T[] {
+	return Array.prototype.concat.apply([], array);
+}
+
+export function coalease<T>(array: ReadonlyArray<T | undefined>): T[] {
+	return <T[]>array.filter(e => !!e);
+}