Hi there!
In your case it does not mean your array is null, 1st because it is not a pointer. The error message just says that the symbol is undefined at the moment the linker tries to find it. Such error usually happens when you try to access a class from an outside class function and the class is not exported. You need to use the module export define name in front of your class name, so anywhere in your code you might have done like below:
UCLASS()
class AMyBLE : public AActor
{
…
}
and you miss:
UCLASS()
class XXXXXXX_API AMyBLE : public AActor
{
…
}
that XXXXXXX_API you will find at the file where you have IMPLEMENT_MODULE(X, Y) or IMPLEMENT_PRIMARY_GAME_MODULE(X, Y, Z), which you should use the Y word there and add the _API suffix.