testing if a node is attached to a physicsBody swift - swift

Question

I am getting the node attached to a contact body (SKPhysicsBody), in a function called while detecting a contact between to SKSpriteNode. Sometimes, I get an error because it can not get the node attached to the contact body, so I test if there's a node to avoid that type of error. But a warning tells me it will never return false. I've not had anymore error like this since I test that but I'm not sure if it works well or if it can still happen. Do you have any idea?
//The actual code
func didBegin(_ contact: SKPhysicsContact) {
if (contact.bodyA.categoryBitMask == enemyCategory) && (contact.bodyB.categoryBitMask == shootCategory){ //test if it is the contact with I want to catch
let shootNode = contact.bodyB.node, shootNode != nil { // I test if there's a node attached to the enemyShootNode but it's supposed never to return false
let enemyNode = contact.bodyA.node, enemyNode != nil { // I test if there's a node attached to the shootNode but it's supposed never to return false
let enemySKNode = enemyNode as? SKSpriteNode
let shootSKNode = shootNode as? SKSpriteNode
// code
}
}
}
}
// The code with error
func didBegin(_ contact: SKPhysicsContact) {
if (contact.bodyA.categoryBitMask == enemyCategory) && (contact.bodyB.categoryBitMask == shootCategory){
let shootNode = contact.bodyB.node!
let enemyNode = contact.bodyA.node! // The error occurs here : "fatal error: unexpectedly found nil while unwrapping an Optional value"
let enemySKNode = enemyNode as? SKSpriteNode
let shootSKNode = shootNode as? SKSpriteNode
}
}

Answer 1

Thanks for your advices, the error indeed comes from the SKPhysics property (the didBegin function is called several times) but I didn't manage to fix.
Although I corrected the way I was checking if a sprite was here, and there are no more warnings or errors so I suppose it works well :
func didBegin(_ contact: SKPhysicsContact) {
if (contact.bodyA.categoryBitMask == enemyCategory) && (contact.bodyB.categoryBitMask == shootCategory) || (contact.bodyA.categoryBitMask == shootCategory) && (contact.bodyB.categoryBitMask == enemyCategory){
if var shootNode = contact.bodyB.node{
if var enemyNode = contact.bodyA.node{
// If the enemyNode and the shootNode don't respectively correspond to
if contact.bodyA.categoryBitMask == shootCategory {
shootNode = contact.bodyA.node!
enemyNode = contact.bodyB.node!
}
let enemySKNode = enemyNode as? SKSpriteNode
let shootSKNode = shootNode as? SKSpriteNode
}
}
}
}