Allow NodeOperator even with NodeRef.value == null

This may be the case on artificial nodes,
such as the artificial roots on
reflexion cities.

Assets/SEE/Controls/Actions/ShowLabel.cs

@@ -181,9 +181,12 @@ private void On()
         /// <seealso cref="SelectionOn"/>
         private void Off()
         {
-            LabelAttributes settings = GetLabelSettings(nodeOperator.Node, nodeOperator.City);
-            nodeOperator.FadeLabel(0f, settings.AnimationFactor);
-            DisplayedLabelOperators.Remove(nodeOperator);
+            if (nodeOperator.Node != null)
+            {
+                LabelAttributes settings = GetLabelSettings(nodeOperator.Node, nodeOperator.City);
+                nodeOperator.FadeLabel(0f, settings.AnimationFactor);
+                DisplayedLabelOperators.Remove(nodeOperator);
+            }
         }
 
         /// <summary>

Assets/SEE/Game/HolisticMetrics/WidgetsManager.cs

@@ -155,8 +155,8 @@ internal void Create(WidgetConfig widgetConfiguration)
                 {
                     ShowNotification.Error("Metric-board error",
                                            "There was an error when displaying the metric on the newly created "
-                                           + $"widget, this is the exception: {exception.Message}");
-                    throw exception;
+                                           + $"widget, this is the exception: {exception.Message}", log: false);
+                    throw;
                 }
             }
         }

Assets/SEE/Game/LabelAttributes.cs

@@ -14,6 +14,16 @@ namespace SEE.Game
     [HideReferenceObjectPicker]
     public class LabelAttributes
     {
+        /// <summary>
+        /// The default value for <see cref="Show"/>.
+        /// </summary>
+        public const float DEFAULT_FONT_SIZE = 0.4f;
+
+        /// <summary>
+        /// The default value for <see cref="Distance"/>.
+        /// </summary>
+        public const float DEFAULT_DISTANCE = 0.2f;
+
         /// <summary>
         /// If true, a label with the node's SourceName will be displayed above each node.
         /// </summary>
@@ -24,13 +34,13 @@ public class LabelAttributes
         /// The distance between the top of the node and its label.
         /// </summary>
         [Tooltip("The distance between the top of the node and its label.")]
-        public float Distance = 0.2f;
+        public float Distance = DEFAULT_DISTANCE;
 
         /// <summary>
         /// The font size of the node's label.
         /// </summary>
         [Tooltip("The font size of the label.")]
-        public float FontSize = 0.4f;
+        public float FontSize = DEFAULT_FONT_SIZE;
 
         /// <summary>
         /// How fast the label should (dis)appear.
@@ -90,4 +100,4 @@ internal void Restore(Dictionary<string, object> attributes, string label)
             }
         }
     }
-}
+}

Assets/SEE/Game/Operator/LabelOperator.cs

@@ -60,7 +60,7 @@ private void PrepareLabel()
             Color textColor = UnityEngine.Color.white;
             Color lineColor = UnityEngine.Color.white;
 
-            string shownText = Node.SourceName;
+            string shownText = Node?.SourceName ?? gameObject.name;
 
             nodeLabel = transform.Find(labelPrefix + shownText)?.gameObject;
             if (nodeLabel == null)
@@ -71,9 +71,10 @@ private void PrepareLabel()
                 // First we create the label.
                 // We define starting and ending positions for the animation.
                 Vector3 startLabelPosition = gameObject.GetTop();
+                float fontSize = Node != null ? City.NodeTypes[Node.Type].LabelSettings.FontSize : LabelAttributes.DEFAULT_FONT_SIZE;
                 nodeLabel = TextFactory.GetTextWithSize(shownText,
                                                         startLabelPosition,
-                                                        City.NodeTypes[Node.Type].LabelSettings.FontSize,
+                                                        fontSize,
                                                         lift: true,
                                                         textColor: textColor);
                 nodeLabel.name = labelPrefix + shownText;
@@ -132,7 +133,7 @@ private Vector3 DesiredLabelTextPosition
                 if (labelAlpha.TargetValue > 0)
                 {
                     // Only put line and label up if the label should actually be shown.
-                    endLabelPosition.y += City.NodeTypes[Node.Type].LabelSettings.Distance;
+                    endLabelPosition.y += Node != null ? City.NodeTypes[Node.Type].LabelSettings.Distance : LabelAttributes.DEFAULT_DISTANCE;
                 }
 
                 return endLabelPosition;
@@ -185,4 +186,4 @@ private Vector3 DesiredLabelEndLinePosition
             nodeLabel.transform.DOMove(position, duration).Play()
         };
     }
-}
+}

Assets/SEE/Game/Operator/NodeOperator.cs

@@ -78,6 +78,8 @@ public partial class NodeOperator : GraphElementOperator<Color>
 
         /// <summary>
         /// The node to which this node operator belongs.
+        ///
+        /// <em>Be aware that this may be null if the node operator is attached to an artificial node.</em>
         /// </summary>
         public Node Node
         {
@@ -461,7 +463,8 @@ Tween[] BlinkAction(int count, float duration)
 
             static Node GetNode(GameObject gameObject)
             {
-                if (!gameObject.TryGetComponent(out NodeRef nodeRef) || nodeRef.Value == null)
+                // We allow a null value for artificial nodes, but at least a NodeRef must be attached.
+                if (!gameObject.TryGetComponent(out NodeRef nodeRef))
                 {
                     throw new InvalidOperationException($"NodeOperator-operated object {gameObject.FullName()} must have {nameof(NodeRef)} attached!");
                 }
@@ -525,4 +528,4 @@ private void Update()
             }
         }
     }
-}
+}