attempt to index a nil value - following tutorial issue

[olongjohnson]

Okay I am completely new and have probably a total brain fart mistake here, but I cannot figure out what I'm doing wrong following the tutorial here: https://wiki.esoui.com/Writing_your_first_addon

I am at the point where FooAddon should be outputting to console when I enter and leave combat, but the line self.inCombat = IsUnitInCombat("player") in FooAddon:Initialize() is throwing an error:

user:/AddOns/FooAddon/FooAddon.lua:6: attempt to index a nil value
stack traceback:
user:/AddOns/FooAddon/FooAddon.lua:6: in function 'FooAddon:Initialize'
user:/AddOns/FooAddon/FooAddon.lua:13: in function 'FooAddon.OnAddonLoaded'
<Locals> event = 65536, addonName = "FooAddon" </Locals>

I've checked for typos - to the point of copy pasting in code from the tutorial, but cannot get this solved. I called and saved IsUnitInCombat("player") to a test variable & printed it to console fine on reload, so I'm assuming my 'self.inCombat' initialization is wrong somehow. I tried initializing the inCombat variable earlier/outside of the initialization function for FooAddon, but that didn't work either.

The only thing I can think to go on now is that this error pops up about 10 times at the bottom of my debug log every reload for various addons, seeming to stem from 'Failed to create control 'LibCustomMenuSubmenu'. Duplicate Name.' following that, there's a bunch of following 'attempt to index a nil value' errors. I'll post a screenshot of my logger output & current lua file.