Fixed small mypy issue when working with application_id

backend/moonstream/routes/subscriptions.py

@@ -99,7 +99,6 @@ async def add_subscription_handler(
     resource_data.update(subscription_data)
 
     try:
-
         resource: BugoutResource = bc.create_resource(
             token=token,
             application_id=MOONSTREAM_APPLICATION_ID,

backend/moonstream/settings.py

@@ -5,8 +5,9 @@ from bugout.app import Bugout
 # Bugout
 bugout_client = Bugout()
 
-MOONSTREAM_APPLICATION_ID = os.environ.get("MOONSTREAM_APPLICATION_ID")
-if MOONSTREAM_APPLICATION_ID is None:
+# Default value is "" instead of None so that mypy understands that MOONSTREAM_APPLICATION_ID is a string
+MOONSTREAM_APPLICATION_ID = os.environ.get("MOONSTREAM_APPLICATION_ID", "")
+if MOONSTREAM_APPLICATION_ID == "":
     raise ValueError("MOONSTREAM_APPLICATION_ID environment variable must be set")
 
 MOONSTREAM_DATA_JOURNAL_ID = os.environ.get("MOONSTREAM_DATA_JOURNAL_ID")