Validates property using .
to represent nested data.
Valid values:
validator.keyNested('foo.bar').validate({foo: {bar: 'foobar'}});
validator.keyNested('foo.bar').validate(
new Map<string, Map<string, string>>([['foo', new Map<string, string>([['bar', 'foobar']])]])
);
Invalid values:
validator.keyNested('foo.bar').validate({foo: {baz: 'bar'}});
validator.keyNested('foo.*').validate({});
validator.keyNested('bar').validate([]);