Steps to reproduce:
1. Open attached “ColliderParent.zip” Unity project
2. Open scene “Example”
3. Enter Play mode
4. Click the red button in Game window

Expected results:
No error appears
Actual results:
Assertion failed error appears after object parent was changed to an object with CompositeCollider2D

Reproduced in: 2018.1.0a7, 2017.3.0f2,, 2017.2.1f1,, 2017.1.2p4, 2017.1.0b4, 5.6.4p4, 5.6.2f1, 5.6.1f1, 5.6.0p3
Didn’t reproduce in: 2017.1.0b3, 5.6.0p2, 5.6.0f1, 5.6.0a1
Regression introduced in: 2017.1.0b4, 5.6.0p3

Error:
Assertion failed: Assertion failed on expression: 'm_CompositeCollider == NULL'
UnityEngine.EventSystems.EventSystem:Update()