[AST] Don’t crash when dumping null ASTNodes
[AST] Don’t crash when dumping null ASTNodes

glessard/swift,JGiola/swift,glessard/swift,roambotics/swift,glessard/swift,apple/swift,apple/swift,JGiola/swift,JGiola/swift,roambotics/swift,apple/swift,roambotics/swift,benlangmuir/swift,apple/swift,glessard/swift,benlangmuir/swift,glessard/swift,benlangmuir/swift,JGiola/swift,benlangmuir/swift,apple/swift,JGiola/swift,apple/swift,roambotics/swift,benlangmuir/swift,roambotics/swift,benlangmuir/swift,JGiola/swift,glessard/swift,roambotics/swift