add no face detection message

app.py

@@ -40,12 +40,14 @@ facenet = init_facenet()
 
 col1, col2, col3 = st.columns([0.2, 2, 0.2])
 
-with col2:
-    img_file_buffer = st.camera_input("")
+with col2: img_file_buffer = st.camera_input("")
 
 if img_file_buffer is not None:
     img = Image.open(img_file_buffer)
     emb = facenet.encode([img])
-    result = index.query(emb[0], top_k=3, include_metadata=True)
-    cards = template.render(results=result["matches"])
-    st.markdown(f"<div class='container-md' align='center'><div class='row'>{cards}</div></div>", unsafe_allow_html=True)
+    if emb:
+        result = index.query(emb[0], top_k=3, include_metadata=True)
+        cards = template.render(results=result["matches"])
+        st.markdown(f"<div class='container-md' align='center'><div class='row'>{cards}</div></div>", unsafe_allow_html=True)
+    else:
+        with col2: st.error('Oops! No face was detected, try again.', icon="🚨")

facenet.py

@@ -15,9 +15,11 @@ class FacenetEmbedder:
     def encode(self, batch):
         face_batch = self.mtcnn(batch)
         face_batch = [i for i in face_batch if i is not None]
-        aligned = torch.stack(face_batch)
-        if self.device.type == "cuda": 
-            aligned = aligned.to(self.device)
+        if face_batch:
+            aligned = torch.stack(face_batch)
+            if self.device.type == "cuda": 
+                aligned = aligned.to(self.device)
 
-        embeddings = self.resnet(aligned).detach().cpu()
-        return embeddings.tolist()
+            embeddings = self.resnet(aligned).detach().cpu()
+            return embeddings.tolist()
+        else: return None