Dashtable case-insensitive filter causes exception when the column contains null value

If a column in the table contains null value at some rows and you try to do a case insensitive filtering like "ine foo', a javascript exception "Cannot read property 'toString' of null" exception" will occur. Apparently it is caused by the line "lhs.toString().toUpperCase()" of fnEval() method in relational.ts failed to check whether lhs (i.e. the cell value) is null or not.

A sample app to reproduce the problem.

from dash import html
from dash import dash_table
import pandas as pd
from collections import OrderedDict

import dash

app = dash.Dash(__name__)

df = pd.DataFrame(OrderedDict([
    ('climate', [None, 'Snowy', 'Sunny', 'Rainy']),
    ('temperature', [13, 43, 50, 30]),
    ('city', ['NYC', None, 'Miami', 'NYC'])
]))


app.layout = html.Div([
    dash_table.DataTable(
        id='table',
        data=df.to_dict('records'),
        columns=[
            {'id': 'climate', 'name': 'climate'},
            {'id': 'temperature', 'name': 'temperature'},
            {'id': 'city', 'name': 'city'},
        ],
        filter_action="native",
    ),
    html.Div(id='table-dropdown-container')
])


if __name__ == '__main__':
    app.run_server(debug=True, port=8051)

Run the app, in the 'city' column header of the table, type in 'ine foo' and hit enter, which should reproduce the problem.

I had a PR for fixing this bug for an old version of dash-table at https://github.com/plotly/dash-table/pull/935/files

Environment:

dash                 2.17.1
dash-core-components 2.0.0
dash-html-components 2.0.0
dash-table           5.0.0

- OS: Ubuntu 22.04
- Browser: Chrome
- Version: 127.0.6533.119

Start in relational.ts at the fnEval() method, then run the supplied Dash sample app and reproduce the case-insensitive filter with null cells. Done means entering a filter such as "ine foo" in the city column no longer raises a JavaScript exception when matching rows contain null values.