Oh, and it's accompanied by this:
ArgumentException: Type cannot be null.
BehaviorDesigner.Editor.TaskInspector.GetInvokeMethodInfo (System.Object task) (at <16f31d5e691e49bb8277da3cfa8e17e2>:0)
BehaviorDesigner.Editor.TaskInspector.CanDrawReflectedField (System.Object task, System.Reflection.FieldInfo field) (at <16f31d5e691e49bb8277da3cfa8e17e2>:0)
BehaviorDesigner.Editor.TaskInspector.DrawObjectFields (BehaviorDesigner.Runtime.BehaviorSource behaviorSource, BehaviorDesigner.Editor.TaskList taskList, BehaviorDesigner.Runtime.Tasks.Task task, System.Object obj, System.Boolean enabled, System.Boolean drawWatch) (at <16f31d5e691e49bb8277da3cfa8e17e2>:0)
BehaviorDesigner.Editor.TaskInspector.DrawTaskFields (BehaviorDesigner.Runtime.BehaviorSource behaviorSource, BehaviorDesigner.Editor.TaskList taskList, BehaviorDesigner.Runtime.Tasks.Task task, System.Boolean enabled) (at <16f31d5e691e49bb8277da3cfa8e17e2>:0)
BehaviorDesigner.Editor.TaskInspector.DrawTaskInspector (BehaviorDesigner.Runtime.BehaviorSource behaviorSource, BehaviorDesigner.Editor.TaskList taskList, BehaviorDesigner.Runtime.Tasks.Task task, System.Boolean enabled) (at <16f31d5e691e49bb8277da3cfa8e17e2>:0)
BehaviorDesigner.Editor.BehaviorDesignerWindow.DrawPropertiesBox () (at <16f31d5e691e49bb8277da3cfa8e17e2>:0)
BehaviorDesigner.Editor.BehaviorDesignerWindow.Draw () (at <16f31d5e691e49bb8277da3cfa8e17e2>:0)
BehaviorDesigner.Editor.BehaviorDesignerWindow.OnGUI () (at <16f31d5e691e49bb8277da3cfa8e17e2>:0)
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <599589bf4ce248909b8a14cbe4a2034e>:0)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <599589bf4ce248909b8a14cbe4a2034e>:0)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at <599589bf4ce248909b8a14cbe4a2034e>:0)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:359)
UnityEditor.HostView.Invoke (System.String methodName) (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:353)
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition, UnityEngine.Rect viewRect) (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:329)
UnityEditor.DockArea.DrawView (UnityEngine.Rect viewRect, UnityEngine.Rect dockAreaRect, System.Boolean floatingWindow, System.Boolean isBottomTab) (at /Users/builduser/buildslave/unity/build/Editor/Mono/GUI/DockArea.cs:374)
UnityEditor.DockArea.OldOnGUI () (at /Users/builduser/buildslave/unity/build/Editor/Mono/GUI/DockArea.cs:341)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:281)
UnityEngine.GUIUtility
rocessEvent(Int32, IntPtr)