This article is a solution If you face an uncaught TypeError which details
explode() expects parameter 2 to be string, null given in /vendor/gene/module-braintree/Model/Lpm/Config.php:127
All you need to do is check the following code & replace the method getAllowedMethods in /vendor/gene/module-braintree/Model/Lpm/Config.php.
public function getAllowedMethods(): array { $this->allowedMethods = []; $allowedMethods = []; if ($this->getValue(self::KEY_ALLOWED_METHODS,$this->storeConfigResolver->getStoreId())) { $allowedMethods = explode(',',$this->getValue(self::KEY_ALLOWED_METHODS,$this->storeConfigResolver->getStoreId())); } foreach ($allowedMethods as $allowedMethod) { $this->allowedMethods[] = [ 'method' => $allowedMethod, 'label' => constant('self::LABEL_'.strtoupper($allowedMethod)), 'countries' => constant('self::COUNTRIES_'.strtoupper($allowedMethod)) ]; } return $this->allowedMethods; }