Gulp 4 task: "Did you forget to signal async completion?"

Setup

λ gulp -v
[10:52:08] CLI version 1.0.0
[10:52:08] Local version 4.0.0-alpha.2

del v2.1.0 Windows 7

Tasks

var del = require('del');
function clean() {
    return del(['docs', 'coverage', 'build', 'release']);
}

function build() {
    return gulp.series(
        clean
    );
}

gulp.task(build);

Error

λ gulp build
[10:52:22] Using gulpfile C:\project\gulpfile.js
[10:52:22] Starting 'build'...
[10:52:22] The following tasks did not complete: build
[10:52:22] Did you forget to signal async completion?

Am I missing something?

[quoniammm]

My suggestion is:

var del = require('del');
function clean(cb) {
    del(['docs', 'coverage', 'build', 'release']);
    cb();
}

gulp.task('build', gulp.series(clean));

[AquilaSagitta]

I did this to solve the issue. Idk why it works it just works

export const build = (done) => {
    gulp.series(clean, gulp.parallel(styles, scripts))(done);
};