protected function _get_boolean_value( $key ) {
		if ( ! isset( $this->types[ $key ] ) || 'boolean' !== $this->types[ $key ] ) {
			return null;
		}

		$default = array_key_exists( $key, $this->defaults ) ? $this->defaults[ $key ] : true;

		// Values are stored as yes/no strings.
		return filter_var( $this->store->get( $key, $default ), FILTER_VALIDATE_BOOLEAN );
	}