assertions method
void
assertions()
assertions before building widget
Implementation
void assertions() {
// text must not contain \x00 character asserting before building
assert(!text.contains('\x00'));
// line Numbers is for only RichText widget as of now
// so both isSelectableText and lineNumbers can't be true one must be false
// not needed anymore
// assert((lineNumbers && isSelectableText) == false);
}