Fix legacy production sheet saving and loading errors (#165)

This fixes #159; I expected `CanBeNull` to be accurate, and in this
case, it wasn't. I also made the reader more forgiving; now it'll
continue to read the rest of the object even if it fails to read one of
the non-constructor properties.

Author: veger

Yafc.Model/Serialization/ErrorCollector.cs

@@ -46,6 +46,9 @@ public void Exception(Exception exception, string message, ErrorSeverity errorSe
             else if (exception is NotSupportedException notSupportedException) {
                 s += notSupportedException.Message;
             }
+            else if (exception is InvalidOperationException unexpectedNull) {
+                s += unexpectedNull.Message;
+            }
             else {
                 s += exception.GetType().Name;
             }

Yafc.Model/Serialization/SerializationMap.cs

@@ -315,7 +315,12 @@ public static void PopulateFromJson(T obj, ref Utf8JsonReader reader, Deserializ
                 }
                 else {
                     _ = reader.Read();
-                    property.DeserializeFromJson(obj, ref reader, allObjects);
+                    try {
+                        property.DeserializeFromJson(obj, ref reader, allObjects);
+                    }
+                    catch (InvalidOperationException ex) {
+                        allObjects.Exception(ex, "Encountered an unexpected value when reading the project file", ErrorSeverity.MajorDataLoss);
+                    }
                 }
                 _ = reader.Read();
             }

Yafc.Model/Serialization/ValueSerializers.cs

@@ -245,6 +245,8 @@ public override void WriteToJson(Utf8JsonWriter writer, PageReference? value) {
         public override void WriteToUndoSnapshot(UndoSnapshotBuilder writer, PageReference? value) {
             writer.WriteManagedReference(value);
         }
+
+        public override bool CanBeNull => true;
     }
 
     internal class TypeSerializer : ValueSerializer<Type> {

changelog.txt

@@ -22,6 +22,7 @@ Date: soon
         - Fix that returning to the Welcome Screen could break the panels in the main window.
         - Make horizontal scrollbar clickable/draggable.
         - Scroll down/up exactly one page with page down/up keys
+        - Fix saving and loading errors with legacy production summaries.
     Internal changes:
         - Initial window size is now separate from the minimal window size.
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