How to fix Error: Panini: rendering error occured. YAMLException: can't read a block mapping entry?

Question

JavaScript

When running gulp in the console, this error arrives. I can't seem to find what's wrong here.
this is part of the cog with panini, where the error comes from.

function html() {
    panini.refresh();
    return src(path.src.html, { base: "app/" })
        .pipe(plumber())
        .pipe(panini({
            root: 'app/',
            layouts: 'app/tpl/layouts/',
            partials: 'app/tpl/partials/',
            helpers: 'app/tpl/helpers/',
            data: 'app/tpl/data/'
        }))
        .pipe(dest(path.build.html))
        .pipe(browsersync.stream());

}

Mistake

Error: Panini: rendering error occured.
YAMLException: can not read a block mapping entry; a multiline key may not be an implicit key at line 4, column 1:

    ^
    at Panini.render (D:\MyProjects\gulp\node_modules\panini\lib\render.js:80:11)
    at DestroyableTransform.Transform._read (D:\MyProjects\gulp\node_modules\readable-stream\lib\_stream_transform.js:184:10)
    at DestroyableTransform.Transform._write (D:\MyProjects\gulp\node_modules\readable-stream\lib\_stream_transform.js:172:83)
    at doWrite (D:\MyProjects\gulp\node_modules\readable-stream\lib\_stream_writable.js:428:64)
    at writeOrBuffer (D:\MyProjects\gulp\node_modules\readable-stream\lib\_stream_writable.js:417:5)
    at DestroyableTransform.Writable.write (D:\MyProjects\gulp\node_modules\readable-stream\lib\_stream_writable.js:334:11)
    at DestroyableTransform.ondata (D:\MyProjects\gulp\node_modules\readable-stream\lib\_stream_readable.js:619:20)
    at DestroyableTransform.emit (events.js:311:20)
    at DestroyableTransform.EventEmitter.emit (domain.js:505:15)
    at addChunk (D:\MyProjects\gulp\node_modules\readable-stream\lib\_stream_readable.js:291:12)
[16:55:25] 'default' errored after 400 ms
[16:55:25] The following tasks did not complete: watchFiles, browserSync, css, js, images
[16:55:25] Did you forget to signal async completion?