None Selected

[hansipie]

Hello,

Defining a selectbox like this :
select = st.selectbox("title", ("A", "B"), index=None)
... I get a KeyError exception at main.py:162
This is caused by the default "None" value. It is changed into an empty space by "replace_empty(...)", but
if selected != st.session_state.state_dict.get(label, None): goes into the "true" statement, and causes an exception.

The fix at main.py:161:
if selected != st.session_state.state_dict.get(label, " "):

I make a PR or let you fix ...