When setting multiselect.key property, empty list is not accepted as an input

[jaceksan]

Summary

I want to set “key” property in multiselects, because it provides me the convenience related to session_state handling.
But, if the input to multiselect is empty, rendering the multiselect fails with the following error:

StreamlitAPIException: Every Multiselect default value must exist in options

Steps to reproduce

Code snippet:

facts = []
st.sidebar.multiselect(
    label="Facts:",
    options=[x.id for x in facts],
    key="selected_facts", # if I comment out this line, it works as expected
)

Expected behavior:

No error is returned.
The input is collected from a backend, it usually is not empty, but it may happen that it’s empty.
I expect the same multiselect declaration works for both scenarios.

Debug info

• Streamlit version: 1.20.0
• Python version: 3.10
• Using PipEnv
• OS version: Ubuntu 22.04
• Browser version: Chrome latest

[ferdy]

I can run your code snippet without issue.

I use windows 10.

The exception message tells us that if the default is defined, the value should be in the options.

Example:

facts = [1, 2, 3]
value = ['a']
st.sidebar.multiselect(
    label="Facts:",
    default=value,
    options=facts,
    key="selected_facts", # if I comment out this line, it works as expected
)

StreamlitAPIException : Every Multiselect default value must exist in options

That is expected as ‘a’ is not in facts.