Returns the Unicode string representing the label on this key.
Do not use the keyLabel to compose a text string: it will be missing special processing for Unicode strings for combining characters and other special characters, and the effects of modifiers.
If you are looking for the character produced by a key event, use RawKeyEvent.character instead.
If you are composing text strings, use the TextField or CupertinoTextField widgets, since those automatically handle many of the complexities of managing keyboard input, like showing a soft keyboard or interacting with an input method editor (IME).
@override String get keyLabel => charactersIgnoringModifiers.isEmpty ? null : charactersIgnoringModifiers;