entry was undefined when using gulp-watch

Crashed on entry.push(file.path);

Crash log:

    C:\env1\node_modules\gulp-webpack\index.js:44
        entry.push(file.path);
              ^
    TypeError: Cannot call method 'push' of undefined
        at Stream.self (C:\env1\node_modules\gulp-webpack\index.js:44:11)
        at Stream.stream.write (C:\env1\node_modules\gulp-webpack\node_modules\through\index.js:26:11)
        at write (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:605:24)
        at flow (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:614:7)
        at Transform.pipeOnReadable (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:646:5)
        at Transform.EventEmitter.emit (events.js:92:17)
        at emitReadable_ (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:430:10)
        at emitReadable (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:426:5)
        at readableAddChunk (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:187:9)
        at Transform.Readable.push (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:149:10)
        at Transform.push (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:145:32)
        at afterTransform (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:101:12)
        at TransformState.afterTransform (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:79:12)
        at Transform.noop [as _transform] (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\through2.js:8:3)
        at Transform._read (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:184:10)
        at Transform._write (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:172:12)
        at doWrite (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_writable.js:238:10)
        at writeOrBuffer (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_writable.js:228:5)
        at Transform.Writable.write (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_writable.js:195:11)
        at write (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:605:24)
        at flow (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:614:7)
        at Transform.pipeOnReadable (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:646:5)
        at Transform.EventEmitter.emit (events.js:92:17)
        at emitReadable_ (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:430:10)
        at emitReadable (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:426:5)
        at readableAddChunk (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:187:9)
        at Transform.Readable.push (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:149:10)
        at Transform.push (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:145:32)
        at afterTransform (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:101:12)
        at TransformState.afterTransform (C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:79:12)
        at C:\env1\node_modules\gulp\node_modules\vinyl-fs\lib\src\getContents\bufferFile.js:12:5
        at evalmachine.<anonymous>:266:14
        at C:\env1\node_modules\gulp\node_modules\vinyl-fs\node_modules\graceful-fs\graceful-fs.js:102:5
        at Object.oncomplete (evalmachine.<anonymous>:107:15)