Update zindex-scatter-image mock

Author: Farkites

test/image/mocks/zindex-scatter-image.json

@@ -11,7 +11,7 @@
         "y0": "F",
         "z": [
         [[1, 0, 0], [0, 1, 0], [0, 0, 1], [0, 0, 0]],
-        [[0, 1, 0], [0, 0, 1], [1, 0, 0], [0, 0, 0]],
+        [[0, 1, 0], [0, null, 1], [1, 0, 0], [0, 0, 0]],
         [[1, 0, 0], [1, 0, 0], [0, 0, 1], [0, 0, 0]]
         ],
         "zindex":10