Update ammeter after circuit element deletion, see #418

js/model/CircuitElement.js

@@ -131,6 +131,11 @@ define( function( require ) {
     // length changes when switching between LIFELIKE |SCHEMATIC
     this.chargePathLength = chargePathLength;
 
+    // The ammeter update is called after items are disposed but before corresponding views are disposed, so we must
+    // take care not to display current for any items that are pending deletion.
+    // See https://github.com/phetsims/circuit-construction-kit-common/issues/418
+    this.circuitElementDisposed = false;
+
     tandem.addInstance( this, TObject, options );
   }
 
@@ -202,6 +207,8 @@ define( function( require ) {
      */
     dispose: function() {
 
+      this.circuitElementDisposed = true;
+
       // Notify about intent to dispose first because dispose listeners may need to access state
       this.disposeEmitter.emit();
       this.disposeEmitter.removeAllListeners();

js/view/AmmeterNode.js

@@ -210,7 +210,11 @@ define( function( require ) {
       for ( var i = 0; i < layer.children.length; i++ ) {
         var circuitElementNode = layer.children[ i ];
         if ( circuitElementNode instanceof CircuitElementNode ) {
-          if ( circuitElementNode.containsSensorPoint( probeNode.translation ) ) {
+
+          // This is called between when the circuit element is disposed and when the corresponding view is disposed
+          // so we must take care not to visit circuit elements that have been disposed but still have a view
+          // see https://github.com/phetsims/circuit-construction-kit-common/issues/418
+          if ( !circuitElementNode.circuitElement.circuitElementDisposed && circuitElementNode.containsSensorPoint( probeNode.translation ) ) {
             return circuitElementNode.circuitElement.currentProperty.get();
           }
         }