Show error when media_player is not media_player

lib/entities/error_entity_widget.dart

@@ -0,0 +1,23 @@
+part of '../main.dart';
+
+class ErrorEntityWidget extends StatelessWidget {
+  
+  final String text;
+
+  ErrorEntityWidget({
+    Key key, this.text
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    final EntityModel entityModel = EntityModel.of(context);
+    String errorText = text ?? "Entity error: ${entityModel.entityWrapper.entity?.entityId}";
+    return Container(
+        child: Padding(
+          padding: EdgeInsets.all(5.0),
+          child: Text(errorText),
+        ),
+        color: Theme.of(context).errorColor,
+    );
+  }
+}