Steps to reproduce:
1.Open attached “wwwheaders.zip" Unity project
2.Open “main” scene
3.Enter Play mode
4.Press “Load Local File” button in Game view

Expected results:
WWW.responseHeaders are printed in Console
Actual results:
NullReferenceException error appears

Reproduced in: 2017.3.0b5, 2017.2.0f3, 2017.1.2p1, 2017.1.0b1
Didn’t reproduce in: 2017.1.0a6
Regression introduced in: 2017.1.0b1

Error:
NullReferenceException: Object reference not set to an instance of an object
UnityEngine.WWW.get_responseHeaders () (at /Users/builduser/buildslave/unity/build/Runtime/WebRequestWWW/UWRWWW.cs:158)
TestLocalLoading+<LoadLocalFile>c__Iterator0.MoveNext () (at Assets/Scripts/TestLocalLoading.cs:20)
UnityEngine.SetupCoroutine.InvokeMoveNext (IEnumerator enumerator, IntPtr returnValueAddress) (at /Users/builduser/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

----------------
Fixed in: 2017.1.2p4, 2017.2.0p3, 2017.3.0b10