fix: Deal with None inputs in transcribe_audio function

app.py

@@ -55,16 +55,23 @@ transcription_fixer = PunctFixer(language="da", device=device)
 
 logger.info("Models loaded, ready to transcribe audio.")
 
-def transcribe_audio(sampling_rate_and_audio: tuple[int, np.ndarray]) -> str:
+def transcribe_audio(sampling_rate_and_audio: tuple[int, np.ndarray] | None) -> str:
     """Transcribe the audio.
 
     Args:
         sampling_rate_and_audio:
-            A tuple with the sampling rate and the audio.
+            A tuple with the sampling rate and the audio, or None if no audio was
+            provided.
 
     Returns:
         The transcription.
     """
+    if sampling_rate_and_audio is None:
+        return (
+            "No audio was provided. Please record or upload an audio clip, and try "
+            "again."
+        )
+
     sampling_rate, audio = sampling_rate_and_audio
     if audio.ndim > 1:
         audio = np.mean(audio, axis=1)