check that healthchecks url is a string and make log message more gen…

…eric

lib/config.py

@@ -56,6 +56,14 @@ def _parse_config(self, config: JSON) -> None:
             if not isinstance(self.check_fares, bool):
                 raise ConfigError("'check_fares' must be a boolean")
 
+        if "healthchecks_url" in config:
+            self.healthchecks_url = config["healthchecks_url"]
+
+            if not isinstance(self.healthchecks_url, str):
+                raise ConfigError("'healthchecks_url' must be a string")
+
+            logger.debug("A Healthchecks URL has been provided")
+
         if "notification_level" in config:
             notification_level = config["notification_level"]
             try:
@@ -97,10 +105,6 @@ def _parse_config(self, config: JSON) -> None:
             # Convert hours to seconds
             self.retrieval_interval *= 3600
 
-        if "healthchecks_url" in config:
-            self.healthchecks_url = config["healthchecks_url"]
-            logger.debug("Setting healthchecks URL to %s", self.healthchecks_url)
-
 
 class GlobalConfig(Config):
     def __init__(self) -> None: