From ac78c50d3108d3e706ad7c510af9f1125f9cd265 Mon Sep 17 00:00:00 2001
From: Gareth Jones <jones258@gmail.com>
Date: Sun, 7 Jul 2019 10:06:16 +1200
Subject: [PATCH] =?UTF-8?q?fix:=20=F0=9F=90=9B=20refactor=20`#writeFile`?=
 =?UTF-8?q?=20to=20be=20compatible=20w/=20`strictNullChecks`?=
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---
 src/volume.ts | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/volume.ts b/src/volume.ts
index ed7be35c..878cc115 100644
--- a/src/volume.ts
+++ b/src/volume.ts
@@ -1255,18 +1255,20 @@ export class Volume {
   writeFile(id: TFileId, data: TData, options: IWriteFileOptions | string, callback: TCallback<void>);
   writeFile(id: TFileId, data: TData, a: TCallback<void> | IWriteFileOptions | string, b?: TCallback<void>) {
     let options: IWriteFileOptions | string = a as IWriteFileOptions;
-    let callback: TCallback<void> = b;
+    let callback: TCallback<void> | undefined = b;
 
     if (typeof a === 'function') {
       options = writeFileDefaults;
       callback = a;
     }
 
+    const cb = validateCallback(callback);
+
     const opts = getWriteFileOptions(options);
     const flagsNum = flagsToNumber(opts.flag);
     const modeNum = modeToNumber(opts.mode);
     const buf = dataToBuffer(data, opts.encoding);
-    this.wrapAsync(this.writeFileBase, [id, buf, flagsNum, modeNum], callback);
+    this.wrapAsync(this.writeFileBase, [id, buf, flagsNum, modeNum], cb);
   }
 
   private linkBase(filename1: string, filename2: string) {