Throw an error for duplicate registrations
Throw an error for duplicate registrations

TypeFox/jupyterlab,jupyter/jupyter-js-ui,eskirk/jupyterlab,TypeFox/jupyterlab,eskirk/jupyterlab,jupyter/jupyterlab,charnpreetsingh185/jupyterlab,TypeFox/jupyterlab,jupyter/jupyter-js-ui,charnpreetsingh185/jupyterlab,jupyter/jupyterlab,charnpreetsingh185/jupyterlab,charnpreetsingh185/jupyterlab,eskirk/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,eskirk/jupyterlab,jupyter/jupyterlab,jupyter/jupyter-js-ui,TypeFox/jupyterlab,eskirk/jupyterlab,TypeFox/jupyterlab,charnpreetsingh185/jupyterlab