Requesting to delete a word throws unexpected error

[indiesquidge]

Requesting to delete a word with some matching prefix to an existing word throws a useful error

const completion = createTrie()

completion.insert('list')
completion.delete('lis') // throws `Error: foo is not a word, nothing deleted`

But if I request to delete a word with no matching prefix to an existing word, the error thrown is not helpful

const completion = createTrie()

completion.delete('foo') // throws `TypeError: Cannot read property 'getIsCompleteString' of undefined`

I would expect the latter snippet to throw the same error as the former snippet.