error correction

app.py

@@ -15,6 +15,7 @@ import streamlit as st
 
 chars = string.digits + string.ascii_uppercase + string.ascii_lowercase + '_$'
 selected_sheet = None
+tabs = None
 
 def compress(g):
     bs = [int(g[i:i + 2], 16) for i in range(0, len(g), 2)]
@@ -131,14 +132,14 @@ if cobie_file_button:
     cobie_file = pd.ExcelFile(cobie_file_path)
     tabs = cobie_file.sheet_names
 
+
+
+if tabs:
     selected_sheet = st.selectbox(
         'Select sheet for changing revit ids to COBie ids',
         tabs,
     )
 
-
-if selected_sheet:
-
     df = cobie_file.parse(selected_sheet)
 
     st.write(df)