The build warnings are harmless, so the actually problem is elsewhere.

It’d be nice if you can find out the entire stacktrace from Emacs for Wrong type argument: stringp, nil.

cider-find-var will prompt me to confirm the var, is this a change in new version? can I disable this?

(defcustom cider-prompt-for-symbol t
  "Controls when to prompt for symbol when a command requires one.

When non-nil, always prompt, and use the symbol at point as the default
value at the prompt.

When nil, attempt to use the symbol at point for the command, and only
prompt if that throws an error."
  :type '(choice (const :tag "always" t)
                 (const :tag "dwim" nil))
  :group 'cider
  :package-version '(cider . "0.9.0"))

shouldn't have changed recently that i know of

@dpsutton thanks! I've just found this, I change it to nil. I'm re-constructing my emacs config, maybe I missed this.

Is there any type of way to auto run tests related to a function when the function is redefined in the repl?

We have the parts for that now.

@bozhidar if the var query code could query for "in use by" this would be trivial.

You would just find usages and filter to tests