Laravel - null value is returned from the database

I get "is null" value from column in database, how to figure out why ?

controler:

public function getValues(Request $request)
    $node_id = floor($day);
    $sub_id = $day;
    $mtime = $request->mtime;
    $silent_data = Auth::user()->lessons()->where('mtime',$mtime)->where('sub_id',$sub_id)->where('node_id',$node_id)->first();

table lessons:

id int(10)
user_id int(10)
node_id int(10)
sub_id varchar(191)
mtime int(10)

laravel console:

select * from `lessons` where `lessons`.`user_id` = 11382 and `lessons`.`user_id` is not null and **`mtime` is null** and `sub_id` = '1.4' and `node_id` = 1

table lessons column mtime has value 10

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