Gulp 4 ReferenceError: merge is not defined

In VS 2019 when I try to Publish to a folder Gulp fails with ReferenceError: merge is not defined.

gulpfile.js

/// <binding AfterBuild='default' />
var gulp = require('gulp');
var uglify = require("gulp-uglify");
var concat = require("gulp-concat");

gulp.task('minify', function () {
    return gulp.src("wwwroot/js/**/*.js")
        .pipe(uglify())
        .pipe(concat("dutchtreat.min.js"))
        .pipe(gulp.dest("wwwroot/dist"));
}); 

var nodeModules = {
  "bootstrap": { "dist/**/*": "" },
  "font-awesome": { "**/*": "" },
  "jquery": { "dist/*": "" },
  "jquery-validation": { "dist/*": "" },
  "jquery-validation-unobstrusive": { "dist/*": "" }  };

gulp.task("node_modules", function () {
let streams = [];

for (var module in nodeModules) {
    console.log("Prepping Scripts for: " + module);
    for (var itemProp in nodeModules[module]) {
        streams.push(gulp.src("node_modules/" + module + "/" + itemProp)
            .pipe(gulp.dest("wwwroot/lib" + module + "/" + nodeModules[module][itemProp])));
    }
}
return merge(streams);
}); 

gulp.task('default', gulp.series("node_modules", "minify")); 

package.json "devDependencies"

"gulp": "4.0.2",
"gulp-uglify": "3.0.2",
"gulp-concat": "2.6.1",
"merge-stream": "2.0.0",
"merge": "1.2.1"

All 5 files are loaded in the Dependencies | npm folder.

Why can it not find merge? Is this syntax correct for Gulp 4?

You need to require merge to use it like you have with everything else.

 var merge = require(“merge-stream”);

I think I usually use gulp-merge but I believe merge-stream will work just as well.