diff --git a/websocket_exporter/probe.py b/websocket_exporter/probe.py
index a95b97e..a7b057e 100644
--- a/websocket_exporter/probe.py
+++ b/websocket_exporter/probe.py
@@ -3,28 +3,29 @@ import logging
 from time import perf_counter
 from typing import Union
 
-from websockets import NegotiationError, client, InvalidStatusCode
+from websockets import InvalidStatusCode, NegotiationError, client
 
-
-EXACT_MATCH = 'exact'
-CONTAINS_MATCH = 'contains'
+EXACT_MATCH = "exact"
+CONTAINS_MATCH = "contains"
 
 
 class ProbResults(object):
     def __init__(self, up: int, latency: float = 0, received: int = 0):
         self.up = up
         self.latency = round(latency, 2)
-        self.received = int(received) if received is not None else "NaN"
+        self.received = int(received) if received is not None else 0
 
     def __str__(self):
         if self.up:
             return f'Websocket up, latency:{self.latency}s, expected response {"" if self.received else "NOT"} received'
-        return f'Webserver DOWN'
+        return f"Webserver DOWN"
 
 
 class WebSocketProbe(object):
 
-    def __init__(self, uri, message=None, expected=None, match=CONTAINS_MATCH, timeout=10):
+    def __init__(
+        self, uri, message=None, expected=None, match=CONTAINS_MATCH, timeout=10
+    ):
         """
         Create a websocket probe that tries establishing a connection and reports the metrics
         :param uri: starts with 'ws://' or ws://
@@ -68,13 +69,17 @@ class WebSocketProbe(object):
         elapsed = 0
         while elapsed < self.timeout:
             try:
-                resp = await asyncio.wait_for(connection.recv(), timeout=(self.timeout-elapsed))
+                resp = await asyncio.wait_for(
+                    connection.recv(), timeout=(self.timeout - elapsed)
+                )
                 if self._match(resp):
                     return True
                 await asyncio.sleep(1)
                 elapsed += 1
             except asyncio.TimeoutError:
-                logging.info(f'Time out while waiting for {self.expected_message} from {self.uri}')
+                logging.info(
+                    f"Time out while waiting for {self.expected_message} from {self.uri}"
+                )
                 return None
         return None