Interesting problem with collision

Object A keeps coming back as null. Feels like I've run through the gauntlet of what it could possibly be. Any suggestions would be greatful. Thanks.

' go through all the attacking missiles looking for a collided image
For Local A:AttackingMissile = EachIn AttackingMissileLst
CollideImage(A.anImage, A.x, A.y, 0, 0, 1, A)
Next

' attacking missile collides with a city
For Local B:Cities = EachIn CitiesLst

Local collided:Object[] = CollideImage(B.anImage, B.x, B.y, 0, 1, 0, Null)

If collided
For Local i = 0 To Len(Collided) - 1
Local A:AttackingMissile = AttackingMissile(Collided[i])
If a = Null
Print "it's null null"
End If
AttackingMissileLst.remove(A)
Next
PlaySound nukeSnd
AddExplosion(B.x, B.y, 1)
B.target = 0
End If
Next