feat(Collection): warn if callback is not function in find and findOne

lib/collection.js

@@ -274,6 +274,11 @@ const DEPRECATED_FIND_OPTIONS = ['maxScan', 'snapshot'];
  * @return {Cursor}
  */
 Collection.prototype.find = function(query, options, callback) {
+  if (typeof callback === 'object') {
+    // TODO(MAJOR): throw in the future
+    console.warn('Third parameter to `find()` must be a callback or undefined');
+  }
+
   let selector = query;
   // figuring out arguments
   if (typeof callback !== 'function') {
@@ -1003,6 +1008,11 @@ Collection.prototype.save = function(doc, options, callback) {
  * @return {Promise} returns Promise if no callback passed
  */
 Collection.prototype.findOne = function(query, options, callback) {
+  if (typeof callback === 'object') {
+    // TODO(MAJOR): throw in the future
+    console.warn('Third parameter to `findOne()` must be a callback or undefined');
+  }
+
   if (typeof query === 'function') (callback = query), (query = {}), (options = {});
   if (typeof options === 'function') (callback = options), (options = {});
   query = query || {};