Crashes on AJV initialized with `meta: false`

[medikoo]

Following will crash with not very descriptive error Error: can't resolve reference http://json-schema.org/draft-07/schema# from id #

const AJV = require('ajv');
const ajv = new AJV({ meta: false });
require('ajv-merge-patch')(ajv);

If it works as intended it'll be good to document that AJV cannot be initialized with meta: false, if we want to take advantage of this plugin

[epoberezkin]

Can be added to docs indeed.