Update app.py

app.py

@@ -414,7 +414,12 @@ elif app_mode == "Data Cleaning":
     if 'cleaned_data' not in st.session_state: #Added a conditional value
         st.session_state.cleaned_data = st.session_state.raw_data.copy()
 
-    df = st.session_state.cleaned_data.copy()
+        # Check and copy cleaned data
+    if st.session_state.cleaned_data is not None:
+        df = st.session_state.cleaned_data.copy()
+    else:
+        st.warning("No cleaned data available. Please perform data cleaning first.")
+    
 
     # --------------------------
     # Data Health Dashboard