When you have Custom Connection and use SelectField, Connection screen becomes unusable (see #17064) 

We should detect the situation and throw an exception when Provider Info is initialized.
airflow/providers_manager.py
if 'get_connection_form_widgets' in hook_class.__dict__:
                widgets = hook_class.get_connection_form_widgets()
                if widgets:
                    self._add_widgets(provider_package, hook_class, widgets)
            if 'get_ui_field_behaviour' in hook_class.__dict__:
                field_behaviours = hook_class.get_ui_field_behaviour()
                if field_behaviours:
                    self._add_customized_fields(provider_package, hook_class, field_behaviours)
        except ImportError as e:
            
            
            log.debug(
                "Exception when importing '%s' from '%s' package: %s",
                hook_class_name,
                provider_package,
                e,
            )
            return
        except Exception as e:
            log.warning(
                "Exception when importing '%s' from '%s' package: %s",
                hook_class_name,
                provider_package,
                e,
            )
            return
        conn_type: str = self._get_attr(hook_class, 'conn_type')
        connection_id_attribute_name: str = self._get_attr(hook_class, 'conn_name_attr')