[BUG] no output callbacks doesn't trigger as initial callback. #3770

from dash import Dash, html, Input, callback

app = Dash()

app.layout = html.Div([
    html.Button("Start", id="start-btn", n_clicks=0),
])


@callback(
    Input("start-btn", "n_clicks"),
)
def update(n_clicks):
    print(f"Clicked {n_clicks}")