Clear out composer cache?

In development (developing a plugin), my create topic button is stuck with a buggy composer.

When I hit the create topic button (anywhere it appears), instead of opening the composer, it gives me this error:

Uncaught Error: Assertion Failed: The key provided to set must be a string or number, you passed undefined

Anyone seen this error before with the composer?

The weird thing about this is that the error continues even if I totally get rid of the code in my plugin.
I think something is happening like this:
–In my plugin, I was trying to add a new topic button to a page, and adding some create composer code.
–probably, there was a typo in that code, and when it went to create the composer, the typo caused the key provided error.
–but, now, that error-ed composer is stuck in the system. So even if I get rid of my plugin code, and try to hit the normal, default create topic buttons, it tries to load that error-ed composer, so even the default buttons send the key provided error when they try to open the composer.

If this is true, I need to refresh the composer / clear out the composer “cache” to move forward. Any way to do this?