Does callback change type of arg?

Dash Python
1

Hello,
I’ve few problems with my code. When I use list in Input - arg children is “NoneType”. If I use single Input I have “list” as a type of children? Why? Does callback change type of arg? My code below:
Input as a list:

        management_page= html.Div([

        dcc.Input(id='name',placeholder='Type a name',type='text',value='name'),
        dcc.Input(id='name1', placeholder='Type a name', type='text', value='name'),
        html.Br(),
        "Choose elements",
        dcc.Dropdown(id='dropd',options=[
            {'label': 'Graph', 'value': 'graph'},
            {'label': 'Textarea', 'value': 'textarea'},
            {'label': 'Datatable', 'value': 'dt'},
        ],
            multi=True),
        html.Button(id='button',children='Nazwa')

])
@app.callback(Output('tabs','children'),[Input('button','n_clicks_timestamp'),Input('name','value')],     [State('tabs','children')]
)
def addNew(click, val,children):
pprint(type(children))
if click is not None:
    tab = dcc.Tab(label='label_t'+str(val), value='val_t' + str(val))
    tab_array.append(tab)
    tab_array_names['value' + str(val)]=Tab('value' + (str(val))).page
    pprint(type(children))
    children+=[tab]
    return children
else:
    pass

Those pprints give: <type ‘list’> <type ‘NoneType’>,then give NoneType everytime.

If I write code like this:

management_page= html.Div([

            dcc.Input(id='name',placeholder='Type a name',type='text',value='name'),
            dcc.Input(id='name1', placeholder='Type a name', type='text', value='name'),
            html.Br(),
            "Choose elements",
            dcc.Dropdown(id='dropd',options=[
                {'label': 'Graph', 'value': 'graph'},
                {'label': 'Textarea', 'value': 'textarea'},
                {'label': 'Datatable', 'value': 'dt'},
            ],
                multi=True),
            html.Button(id='button',children='Nazwa')

])
@app.callback(Output('tabs','children'),Input('button','n_clicks_timestamp'),[State('tabs','children')]
)
def addNew(click,children):
    pprint(type(children))
    if click is not None:
        tab = dcc.Tab(label='label_t'+str("x"), value='val_t' + str("x"))
        tab_array.append(tab)
        tab_array_names['value' + str("x")]=Tab('value' + (str("x"l))).page
        pprint(type(children))
        children+=[tab]
        #children.append(tab)
        pprint(type(children))

        return children
    else:
        pass

Give me <type ‘list’> everytime.
Anyone knows why?