NullReferenceException when opening PointerProfile without main camera in scene

[jloehr]

Describe the bug

Opening the PointerProfile while there is no main camera in the currently opened scene, results in a NullReferenceException and the inspector failing to render the profile inspector.

To reproduce

Steps to reproduce the behavior:

1. Open or create a scene in the Unity Editor without a main camera.
2. Navigate to the custom or default profile (Can be any higher level profile, which also renders the PointerProfile inspector)
3. In the Input profile unfold the Pointer inspector.
4. Observe the Inspector rendering collapsing and several NullReferenceExpections being thrown in the console.

Expected behavior

PointerProfile is correctly rendered in the inspector.

Screenshots

Inspector:

Log after unfolding the PointerProfile

[10:31:23] No main camera found. Searching for cameras in the scene.
[10:31:23] The Mixed Reality Toolkit was unable to determine a main camera. Please tag the scene's primary camera as "MainCamera", in the hierarchy.
[10:31:23] NullReferenceException: Object reference not set to an instance of an object

StackTrace for the NullReferenceException:

NullReferenceException: Object reference not set to an instance of an object
Microsoft.MixedReality.Toolkit.Input.Editor.MixedRealityPointerProfileInspector.OnInspectorGUI () (at Assets/Plugins/MRTK/Core/Inspectors/Profiles/MixedRealityPointerProfileInspector.cs:113)
Microsoft.MixedReality.Toolkit.Utilities.Editor.MixedRealityInspectorUtility.DrawSubProfileEditor (UnityEngine.Object profileObject, System.Boolean renderProfileInBox) (at Assets/Plugins/MRTK/Core/Inspectors/Utilities/MixedRealityInspectorUtility.cs:540)
Microsoft.MixedReality.Toolkit.Editor.BaseMixedRealityProfileInspector.RenderProfileInternal (UnityEditor.SerializedProperty property, System.Type profileType, System.Boolean showCloneButton, System.Boolean renderProfileInBox, System.Type serviceType, System.Boolean profileRequiredOverride) (at Assets/Plugins/MRTK/Core/Inspectors/Profiles/BaseMixedRealityProfileInspector.cs:151)
Microsoft.MixedReality.Toolkit.Editor.BaseMixedRealityProfileInspector.RenderProfile (UnityEditor.SerializedProperty property, System.Type profileType, System.Boolean showCloneButton, System.Boolean renderProfileInBox, System.Type serviceType, System.Boolean profileRequiredOverride) (at Assets/Plugins/MRTK/Core/Inspectors/Profiles/BaseMixedRealityProfileInspector.cs:80)
Microsoft.MixedReality.Toolkit.Input.Editor.MixedRealityInputSystemProfileInspector+<>c__DisplayClass34_0.<OnInspectorGUI>b__2 () (at Assets/Plugins/MRTK/Core/Inspectors/Profiles/MixedRealityInputSystemProfileInspector.cs:121)
Microsoft.MixedReality.Toolkit.Editor.BaseMixedRealityProfileInspector.RenderFoldout (System.Boolean& currentState, System.String title, System.Action renderContent, System.String preferenceKey) (at Assets/Plugins/MRTK/Core/Inspectors/Profiles/BaseMixedRealityProfileInspector.cs:183)
Microsoft.MixedReality.Toolkit.Input.Editor.MixedRealityInputSystemProfileInspector.OnInspectorGUI () (at Assets/Plugins/MRTK/Core/Inspectors/Profiles/MixedRealityInputSystemProfileInspector.cs:117)
Microsoft.MixedReality.Toolkit.Utilities.Editor.MixedRealityInspectorUtility.DrawSubProfileEditor (UnityEngine.Object profileObject, System.Boolean renderProfileInBox) (at Assets/Plugins/MRT

Your setup

• Unity 2020.3.20f1
• MRTK 2.8.2

Target platform

• Editor

Additional context

The throwing line is MixedRealityPointerProfileInspector.cs#L113, which makes the assumption that the Main Camera is always available.

[jloehr]

Just updated the issue, the exception is thrown if there is a camera in the scene, but none is tagged as main camera.
Moreover if there actually is no camera at all in the scene, the profile simply adds a new one, which may be undesired in certain situations as well.