I can no longer see any brushes in the default terrain view. Does anyone have a clue as to what is going on and how I can fix this bug? Currently using 2018.3.0b1
UnassignedReferenceException: The variable m_Mask of Brush has not been assigned.
You probably need to assign the m_Mask variable of the Brush script in the inspector.
UnityEditor.Brush.GenerateBrushTexture (UnityEngine.Texture2D mask, UnityEngine.AnimationCurve falloff, System.Single radiusScale, System.Int32 width, System.Int32 height, System.Boolean isThumbnail) (at C:/buildslave/unity/build/Modules/TerrainEditor/Brush/Brush.cs:116)
UnityEditor.Brush.UpdateThumbnail () (at C:/buildslave/unity/build/Modules/TerrainEditor/Brush/Brush.cs:63)
UnityEditor.Brush.get_thumbnail () (at C:/buildslave/unity/build/Modules/TerrainEditor/Brush/Brush.cs:69)
UnityEditor.BrushList.GUIContentFromBrush (UnityEditor.Brush[] brushes) (at C:/buildslave/unity/build/Modules/TerrainEditor/Brush/BrushList.cs:238)
UnityEditor.BrushList.BrushSelectionGrid (System.Int32 selected, UnityEditor.Brush[] brushes, System.Int32 approxSize, UnityEngine.GUIStyle style, UnityEngine.GUIContent emptyString, System.Boolean& doubleClick) (at C:/buildslave/unity/build/Modules/TerrainEditor/Brush/BrushList.cs:206)
UnityEditor.BrushList.ShowGUI () (at C:/buildslave/unity/build/Modules/TerrainEditor/Brush/BrushList.cs:119)
UnityEditor.TerrainInspector.ShowBrushes (System.Int32 spacing) (at C:/buildslave/unity/build/Modules/TerrainEditor/TerrainInspector.cs:1405)
UnityEditor.Experimental.TerrainAPI.OnInspectorGUIContext.ShowBrushesGUI (System.Int32 spacing) (at C:/buildslave/unity/build/Modules/TerrainEditor/PaintTools/TerrainPaintTool.cs:120)
UnityEditor.Experimental.TerrainAPI.PaintTextureTool.OnInspectorGUI (UnityEngine.Terrain terrain, UnityEditor.Experimental.TerrainAPI.IOnInspectorGUI editContext) (at C:/buildslave/unity/build/Modules/TerrainEditor/PaintTools/PaintTextureTool.cs:139)
UnityEditor.TerrainInspector.ShowPaint () (at C:/buildslave/unity/build/Modules/TerrainEditor/TerrainInspector.cs:1398)
UnityEditor.TerrainInspector.OnInspectorGUI () (at C:/buildslave/unity/build/Modules/TerrainEditor/TerrainInspector.cs:1752)
UnityEditor.InspectorWindow.DoOnInspectorGUI (System.Boolean rebuildOptimizedGUIBlock, UnityEditor.Editor editor, System.Boolean wasVisible, UnityEngine.Rect& contentRect) (at C:/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:1599)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)