In Unity 2017.3.0f3 this happens after modifying Wwise project and returning to unity. Not sure where to file a bug report, so I'm posting it here.
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.InspectorWindow.OnSelectionChange () (at C:/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:147)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:295)
UnityEditor.HostView.Invoke (System.String methodName) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:288)
UnityEditor.HostView.OnSelectionChange () (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:168)
UnityEditor.AssetDatabase:CreateAsset(Object, String)
AkWwiseProjectInfo:GetData() (at Assets/Wwise/Editor/WwiseWindows/AkWwiseProjectInfo.cs:38)
AkWwiseTreeView:GetExpansionStatus(String) (at Assets/Wwise/Editor/WwiseWindows/AkWwiseTreeView.cs:501)
AkWwiseTreeView:SetRootItem(String, WwiseObjectType) (at Assets/Wwise/Editor/WwiseWindows/AkWwiseTreeView.cs:106)
AkWwisePicker:PopulateTreeview() (at Assets/Wwise/Editor/WwiseWindows/AkWwisePicker.cs:113)
AkWwiseTreeView:SaveExpansionStatus() (at Assets/Wwise/Editor/WwiseWindows/AkWwiseTreeView.cs:465)
AkWwisePicker:OnEnable() (at Assets/Wwise/Editor/WwiseWindows/AkWwisePicker.cs:48)