In "Image Filter Stack", under the Aspect Property continuously NullReferenceException is thrown on editing the "Remap Curve ", refer attached video.

Steps to repro:
1. Create a new project
2. Windows > Package Manager > TerrainTools > Install
3. Project > right-click > Create > Image Filter Stack
4. Project > Image Filter Stack > Inspector > add Aspect Property
5. Inspector > Aspect Property > Remap Curve > Click > Remap Curve Window Open > Edit Curve

Actual Result:
NullReferenceException is thrown on editing the Remap Curve in the Image Filter Stack

Expected Result:
No errors in the console while editing Remap Curve

Reproducible in:
2020.2.0a14, 2020.1.0b12, 2019.3.14f1 with Package Version 3.0.1, 3.0.0 , 2.0.2, 2.0.1, 2.0.0
2019.2.0a1 with Package Version 2.0.0

Note: Image Filter Stack is introduced in Package version 2.0.0

Environment:
Windows 10 & macOS 10.14

Stack Trace:
NullReferenceException: Object reference not set to an instance of an object
TerrainTools.Utility.AnimationCurveToRenderTexture (UnityEngine.AnimationCurve curve, UnityEngine.Texture2D& tex) (at library/packagecache/com.unity.terrain-tools@3.0.1-preview/editor/terraintools/terraintoolutility.cs:11)
UnityEditor.Experimental.TerrainAPI.AspectFilter.DoGUI (UnityEngine.Rect rect) (at library/packagecache/com.unity.terrain-tools@3.0.1-preview/editor/terraintools/filterstack/aspectfilter.cs:99)
UnityEditor.Experimental.TerrainAPI.FilterStackView.DrawElementCB (UnityEngine.Rect totalRect, System.Int32 index, System.Boolean isActive, System.Boolean isFocused) (at library/packagecache/com.unity.terrain-tools@3.0.1-preview/editor/terraintools/filterstack/filterstackview.cs:473)
UnityEditorInternal.ReorderableList.DoListElements (UnityEngine.Rect listRect, UnityEngine.Rect visibleRect) (at <d152ba57ae03448bbfbedbdc3373ab44>:0)
UnityEditorInternal.ReorderableList.DoLayoutList () (at <d152ba57ae03448bbfbedbdc3373ab44>:0)
UnityEditor.Experimental.TerrainAPI.FilterStackView.OnGUI () (at library/packagecache/com.unity.terrain-tools@3.0.1-preview/editor/terraintools/filterstack/filterstackview.cs:168)
UnityEditor.Experimental.TerrainAPI.FilterStackEditor.OnInspectorGUI () (at library/packagecache/com.unity.terrain-tools@3.0.1-preview/editor/terraintools/filterstack/editor/filterstackeditor.cs:18)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass58_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <b19f2d0e874747f7af081cc4f93109d2>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)