toNum method
Converts the value to a num if possible.
Returns the value as num if it's already a num,
or attempts to parse it if it's a String.
Returns null
if conversion is not possible.
Implementation
num? toNum() {
if (this is num) {
return this as num;
} else if (this is String) {
return num.tryParse(this as String);
}
return null;
}