Assertion Failed: '@dropdown.isOpen' is not a valid path

Getting this error when trying to run a web app built in ember:

Template Compiler Error (broccoli-persistent-filter:TemplateCompiler) in ember-basic-dropdown/templates/components/basic-dropdown-content.hbs

Assertion Failed: '@dropdown.isOpen' is not a valid path. ('ember-basic-dropdown/templates/components/basic-dropdown-content.hbs' @ L2:C6)

Using:

ember-cli: 2.18.2
node: 10.15.2
os: linux x64
ember-basic-dropdown: 5.8.0

Full Error Log