How to fill entry with missing when nothing was writte in in xamarin app?

Issue

I am doing Import page and if user leave some entry blank and click on import button I want to fill blank entries with Missing. I have tried that like this:

if (liveryEntry.Text == null)
            {
                liveryEntry.Text = "Missing";
            }
            if (registrationEntry.Text == null)
            {
                registrationEntry.Text = "Missing";
            }
            if (airportEntry == null)
            {
                airportEntry.Text = "Missing";
            }                
            if (commentEntry == null)
            {
                commentEntry.Text = "Missing";
            }

But sometimes it works and fill it with Missing, sometimes it doesnt work. What is wrong or is there another way to do that? Here is full code of method:

private async void buttonImport_Clicked(object sender, EventArgs e)
    {
        var db = new SQLiteConnection(_dbPath);
        db.CreateTable<Airplane>();
        collectionPlane.IsVisible = false;
        collectionAirline.IsVisible = false;
        collectionLivery.IsVisible = false;
        collectionRegistration.IsVisible = false;
        collectionAirport.IsVisible = false;
        try
        {
            if (liveryEntry.Text == null)
            {
                liveryEntry.Text = "Missing";
            }
            if (registrationEntry.Text == null)
            {
                registrationEntry.Text = "Missing";
            }
            if (airportEntry == null)
            {
                airportEntry.Text = "Missing";
            }                
            if (commentEntry == null)
            {
                commentEntry.Text = "Missing";
            }
            if (planeEntry.Text != null && airlineEntry.Text != null)
            {
                var url = PhotoPick();
                int i = 1;
                int same = 0;
                string fileName = registrationEntry.Text;
                for (int b = 1; b <= GetNumberPhotos(); b++)
                {
                    if (db.Table<Airplane>().FirstOrDefault(d => d.Id == b) != null)
                    {
                        var rowData = db.Table<Airplane>().FirstOrDefault(d => d.Id == b);
                        string match = rowData.Registration;
                        if (fileName == match)
                        {
                            same++;
                        }
                    }
                }
                i = 1 + same;
                fileName = registrationEntry.Text + "-" + i;
                var thumbUrl = CreateThumbnail(await url, fileName);
                var maxPK = db.Table<Airplane>().OrderByDescending(c => c.Id).FirstOrDefault();
                Airplane airplane = new Airplane()
                {
                    Id = (maxPK == null ? 1 : maxPK.Id + 1),
                    SearchId = planeEntry.Text + airlineEntry.Text + liveryEntry.Text + registrationEntry.Text + airportEntry.Text + datePicker.Date.ToString() + commentEntry.Text,
                    Plane = planeEntry.Text.ToUpper(),
                    Airline = airlineEntry.Text,
                    Livery = liveryEntry.Text,
                    Registration = registrationEntry.Text.ToUpper(),
                    Airport = airportEntry.Text.ToUpper(),
                    Date = datePicker.Date,
                    Comment = commentEntry.Text,
                    Url = await url,
                    ThumbnailUrl = thumbUrl
                };
                db.Insert(airplane);
                await DisplayAlert("Saved", planeEntry.Text + " of " + airlineEntry.Text + " is saved.", "OK");
                planeEntry.Text = "";
                airlineEntry.Text = "";
                liveryEntry.Text = "";
                registrationEntry.Text = "";
                airportEntry.Text = "";                    
                commentEntry.Text = "";
            }
            else
                await DisplayAlert("Fill all needed fields", "You have to fill all fields except livery and comment", "OK");
        }
        catch
        {
            await DisplayAlert("Error", "Something went wrong", "Try again");
        }
    }

Solution

It is probably some kind of bug or missunderstanding @Cfun have solved with if ( string.IsNullOrEmpty(liveryEntry.Text)) and it works as expected.

Answered By - Lukáš Matoušek