Incorrect $sourcePath in BootstrapAsset.php

My first go at a projet using bootstrap 4 is failling with...

Invalid Argument – yii\base\InvalidArgumentException

The file or directory to be published does not exist: /path/to/vendor/npm/bootstrap/dist

The following trace points to yiisoft/yii2-bootstrap4/src/Nav.php which loads yiisoft/yii2-bootstrap4/src/BootstrapAsset.php which has...

class BootstrapAsset extends AssetBundle
{
    public $sourcePath = '@npm/bootstrap/dist';
    public $css = [
        'css/bootstrap.css',
    ];
}

However the NPM package is installed at vendor/npm-asset which is in keeping with yiisoft/yii2-bootstrap4/composer.json which has...

    "require": {
        "yiisoft/yii2": "~2.0",
        "npm-asset/bootstrap": "^4.3"
    },

Shouldn't that $sourcePath be @npm-asset/bootstrap/dist?

yiisoft / yii2-bootstrap4