FormBuilderValidators.equal() not working with form state?

[orbiteleven]

Using form_builder_validators with flutter_form_builder and I have what I think should be a pretty common password+confirm password form, but I'm a bit confused. This is what I have so far:

FormBuilderTextField(
    name: 'password',
    decoration: InputDecoration(labelText: 'Password'),
    obscureText: true,
    validator: FormBuilderValidators.compose([
      FormBuilderValidators.required(),
      FormBuilderValidators.minLength(6)
    ])),
FormBuilderTextField(
    name: 'confirmPassword',
    decoration: InputDecoration(labelText: 'Confirm Password'),
    obscureText: true,
    validator: FormBuilderValidators.compose([
      FormBuilderValidators.required(),
      FormBuilderValidators.minLength(6),
      (value) {
        print(
            "value: $value matches ${_formKey.currentState?.instantValue['password']}");
        return null;
      },
      FormBuilderValidators.equal(
          _formKey.currentState?.instantValue['password'] ?? '',
          errorText: 'Passwords do not match')
    ])),

the "custom" validator works fine, but FormBuilderValidators.equal() throws an error. What am I doing wrong?

[deandreamatias]

I will close because create a issue #63 , but is a interesting bug