Fix type-cast error when deserializing a widget's size (flutter#8343)

Author: elliette

packages/devtools_app/lib/src/screens/inspector_v2/inspector_data_models.dart

@@ -127,6 +127,7 @@ class LayoutProperties {
         children = copyLevel == 0
             ? []
             : node.childrenNow
+                .where((child) => child.size != null)
                 .map(
                   (child) => LayoutProperties(child, copyLevel: copyLevel - 1),
                 )

packages/devtools_app/lib/src/shared/diagnostics/diagnostics_node.dart

@@ -75,10 +75,13 @@ class RemoteDiagnosticsNode extends DiagnosticableTree {
       );
   }
 
-  static Size deserializeSize(Map<String, Object> json) {
+  static Size? deserializeSize(Map<String, Object> json) {
+    final width = json['width'] as String?;
+    final height = json['height'] as String?;
+    if (width == null || height == null) return null;
     return Size(
-      double.parse(json['width'] as String),
-      double.parse(json['height'] as String),
+      double.parse(width),
+      double.parse(height),
     );
   }
 
@@ -461,6 +464,7 @@ class RemoteDiagnosticsNode extends DiagnosticableTree {
     if ((!forFlexLayout && !isBoxLayout) || (forFlexLayout && !isFlexLayout)) {
       return null;
     }
+    if (size == null) return null;
     return forFlexLayout
         ? FlexLayoutProperties.fromDiagnostics(this)
         : LayoutProperties(this);