QGIS » QGIS Application

Cannot reproduce on master/linux with Qt 5.9.3

I'm sending part of code:

def vloz_kere(dialog, layer, feature):
  global myDialog
  myDialog = dialog
  fTAXON = dialog.findChild(QComboBox, "TAXON")
    fTAXON.editTextChanged.connect(refresh_combo)

def refresh_combo():
    fTAXON = myDialog.findChild(QComboBox, "TAXON")
    if fTAXON.count() is None or fTAXON.count() == 0 :
        pass
    else:
        fTAXON.clear() 
    for key, value in druh.items():
        if str(fTAXON.currentText()) in value:
            fTAXON.addItem(value)

I try add condition for first use (fTAXON.count() is None or 0) but problem is not finished. Qgis frozes and be shutdown with no debug infrormations.

The problem occurs after start attribute form when i try type something in combobox, cursor is freeze for 3 - 4 seconds and the application crashes.