On dragging the Signal on Control track assets throw InvalidOperationException, refer to the attached video.

Steps to reproduce:
1. Create a new project
2. Window > Package Manager > Timeline(preview.7 - 1.3.0) > Install
3. Window > Sequencing > Timeline
4. Create a Playable Director and Timeline Asset for Cube
5. Create Control Track and add Control Clip from GameObject
6. Project > Right-Click > Create >Signal
7. Drag Signal on Control Track assets

Actual Result:
InvalidOperationException is thrown on dragging the Signal on Control track assets

Expected Result:
No error in Console

Tested on Unity version:
2020.1.0a25, 2019.3.2f1, 2019.3.0a1

Package version occurring: preview.7 - 1.3.0, 1.2.12, 1.2.6

Environment:
Windows 10 and macOS 10.14

Stack trace:
InvalidOperationException: Markers implementing the INotification interface cannot be added on tracks that do not support notifications
UnityEngine.Timeline.MarkerList.CreateMarker (System.Type type, System.Double time, UnityEngine.Timeline.TrackAsset owner) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/runtime/events/markerlist.cs:117)
UnityEngine.Timeline.TrackAsset.CreateMarker (System.Type type, System.Double time) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/runtime/trackasset.cs:527)
UnityEditor.Timeline.TimelineHelpers.CreateMarkerOnTrack (System.Type markerType, UnityEngine.Object assignableObject, UnityEngine.Timeline.TrackAsset parentTrack, System.Double candidateTime) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/timelinehelpers.cs:687)
UnityEditor.Timeline.TimelineHelpers.CreateMarkersFromObjects (System.Type assetType, UnityEngine.Timeline.TrackAsset targetTrack, System.Double candidateTime, System.Collections.Generic.IEnumerable`1[T] objects) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/timelinehelpers.cs:665)
UnityEditor.TimelineDragging+<>c__DisplayClass24_0.<HandleItemCreation>b__1 (System.Type assetType) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/treeview/timelinedragging.cs:444)
UnityEditor.TimelineDragging.HandleItemCreation (System.Collections.Generic.IEnumerable`1[T] objectsBeingDropped, UnityEngine.Timeline.TrackAsset targetTrack, System.Double candidateTime, UnityEditor.TimelineDragging+TypeResolver typeResolver, System.Boolean allowMenu) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/treeview/timelinedragging.cs:454)
UnityEditor.TimelineDragging.HandleClipPaneObjectDragAndDrop (System.Collections.Generic.IEnumerable`1[T] objectsBeingDropped, UnityEngine.Timeline.TrackAsset targetTrack, System.Boolean perform, UnityEngine.Timeline.TimelineAsset timeline, UnityEngine.Timeline.TrackAsset parent, UnityEngine.Playables.PlayableDirector director, System.Double candidateTime, UnityEditor.TimelineDragging+TypeResolver typeResolver, UnityEngine.Timeline.TrackAsset insertBefore) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/treeview/timelinedragging.cs:406)
UnityEditor.TimelineDragging.DoDrag (UnityEditor.IMGUI.Controls.TreeViewItem parentItem, UnityEditor.IMGUI.Controls.TreeViewItem targetItem, System.Boolean perform, UnityEditor.IMGUI.Controls.TreeViewDragging+DropPosition dropPos) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/treeview/timelinedragging.cs:271)
UnityEditor.IMGUI.Controls.TreeViewDragging.DragElement (UnityEditor.IMGUI.Controls.TreeViewItem targetItem, UnityEngine.Rect targetItemRect, System.Int32 row) (at <ab8137009875411cacde450b0cedf54f>:0)
UnityEditor.TimelineDragging.DragElement (UnityEditor.IMGUI.Controls.TreeViewItem targetItem, UnityEngine.Rect targetItemRect, System.Int32 row) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/treeview/timelinedragging.cs:141)
UnityEditor.IMGUI.Controls.TreeViewController.HandleUnusedMouseEventsForItem (UnityEngine.Rect rect, UnityEditor.IMGUI.Controls.TreeViewItem item, System.Int32 row) (at <ab8137009875411cacde450b0cedf54f>:0)
UnityEditor.IMGUI.Controls.TreeViewController.DoItemGUI (UnityEditor.IMGUI.Controls.TreeViewItem item, System.Int32 row, System.Single rowWidth, System.Boolean hasFocus) (at <ab8137009875411cacde450b0cedf54f>:0)
UnityEditor.IMGUI.Controls.TreeViewController.IterateVisibleItems (System.Int32 firstRow, System.Int32 numVisibleRows, System.Single rowWidth, System.Boolean hasFocus) (at <ab8137009875411cacde450b0cedf54f>:0)
UnityEditor.IMGUI.Controls.TreeViewController.OnGUI (UnityEngine.Rect rect, System.Int32 keyboardControlID) (at <ab8137009875411cacde450b0cedf54f>:0)
UnityEditor.Timeline.TimelineTreeViewGUI.OnGUI (UnityEngine.Rect rect) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/treeview/timelinetreeviewgui.cs:152)
UnityEditor.Timeline.TimelineWindow.DrawTracksGUI (UnityEngine.Rect clientRect, UnityEditor.Timeline.TimelineModeGUIState trackState) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/window/timelinewindow_trackgui.cs:173)
UnityEditor.Timeline.TimelineWindow.TracksGUI (UnityEngine.Rect clientRect, UnityEditor.Timeline.WindowState state, UnityEditor.Timeline.TimelineModeGUIState trackState) (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/window/timelinewindow_trackgui.cs:47)
UnityEditor.Timeline.TimelineWindow.TrackViewsGUI () (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/window/timelinewindow_gui.cs:173)
UnityEditor.Timeline.TimelineWindow.SequencerGUI () (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/window/timelinewindow_gui.cs:265)
UnityEditor.Timeline.TimelineWindow.DoLayout () (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/window/timelinewindow_gui.cs:148)
UnityEditor.Timeline.TimelineWindow.OnGUI () (at library/packagecache/com.unity.timeline@1.3.0-preview.7/editor/window/timelinewindow.cs:232)
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition, UnityEngine.Rect viewRect) (at <ab8137009875411cacde450b0cedf54f>:0)
UnityEditor.DockArea.DrawView (UnityEngine.Rect viewRect, UnityEngine.Rect dockAreaRect) (at <ab8137009875411cacde450b0cedf54f>:0)
UnityEditor.DockArea.OldOnGUI () (at <ab8137009875411cacde450b0cedf54f>:0)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Action onGUIHandler, System.Boolean canAffectFocus) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, UnityEngine.Matrix4x4 worldTransform, UnityEngine.Rect clippingRect, System.Action onGUIHandler, System.Boolean canAffectFocus) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, System.Action onGUIHandler, System.Boolean canAffectFocus) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, System.Boolean canAffectFocus) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.IMGUIContainer.SendEventToIMGUIRaw (UnityEngine.UIElements.EventBase evt, System.Boolean canAffectFocus, System.Boolean verifyBounds) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.IMGUIContainer.SendEventToIMGUI (UnityEngine.UIElements.EventBase evt, System.Boolean canAffectFocus, System.Boolean verifyBounds) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.IMGUIContainer.HandleEvent (UnityEngine.UIElements.EventBase evt) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.EventDispatchUtilities.PropagateEvent (UnityEngine.UIElements.EventBase evt) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.MouseEventDispatchingStrategy.SendEventToRegularTarget (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.MouseEventDispatchingStrategy.SendEventToTarget (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.MouseEventDispatchingStrategy.DispatchEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.EventDispatcher.ApplyDispatchingStrategies (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel, System.Boolean imguiEventIsInitiallyUsed) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.EventDispatcher.Dispatch (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.IPanel panel, UnityEngine.UIElements.DispatchMode dispatchMode) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.BaseVisualElementPanel.SendEvent (UnityEngine.UIElements.EventBase e, UnityEngine.UIElements.DispatchMode dispatchMode) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& eventHandled) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.UIEventRegistration.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.UIElements.UIEventRegistration+<>c.<.cctor>b__1_2 (System.Int32 i, System.IntPtr ptr) (at <7b3a83bb6c544eadaab9a841ae1beea3>:0)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& result) (at <fa83d136cc594919bea78eaa8421fde3>:0)