Previous fix to using existing collections in MongoLRUReader wasn't w…

…orking. This should do it.

locust_plugins/mongoreader.py

@@ -34,7 +34,7 @@ def __init__(
 
         """
         self.timestamp_field = timestamp_field
-        if not coll:
+        if coll is None:
             self.coll: Collection = MongoClient(env["LOCUST_MONGO"])[env["LOCUST_MONGO_DATABASE"]][
                 env["LOCUST_MONGO_COLLECTION"]
             ]