fix errors reading empty JSON files

docs/release-notes.md

@@ -8,6 +8,7 @@
   * Removed experimental 'aggressive memory optimizations' option.  
     _This was disabled by default and is no longer needed in most cases. Memory usage will be better reduced by reworked asset propagation in the upcoming SMAPI 4.0.0._
   * Fixed 'content file was not found' error when the game tries to load unlocalized text from a localizable mod data asset.
+  * Fixed error reading empty JSON files. These are now treated as if they didn't exist like before 3.14.0.
   * Updated compatibility list.
 
 ## 3.14.0

src/SMAPI.Toolkit/Serialization/JsonHelper.cs

@@ -108,12 +108,11 @@ namespace StardewModdingAPI.Toolkit.Serialization
         /// <summary>Deserialize JSON text if possible.</summary>
         /// <typeparam name="TModel">The model type.</typeparam>
         /// <param name="json">The raw JSON text.</param>
-        public TModel Deserialize<TModel>(string json)
+        public TModel? Deserialize<TModel>(string json)
         {
             try
             {
-                return JsonConvert.DeserializeObject<TModel>(json, this.JsonSettings)
+                return JsonConvert.DeserializeObject<TModel>(json, this.JsonSettings);
-                    ?? throw new InvalidOperationException($"Couldn't deserialize model type '{typeof(TModel)}' from empty or null JSON.");
             }
             catch (JsonReaderException)
             {

src/SMAPI/Framework/SMultiplayer.cs

@@ -9,6 +9,7 @@ using StardewModdingAPI.Events;
 using StardewModdingAPI.Framework.Events;
 using StardewModdingAPI.Framework.Networking;
 using StardewModdingAPI.Framework.Reflection;
+using StardewModdingAPI.Internal;
 using StardewModdingAPI.Toolkit.Serialization;
 using StardewModdingAPI.Utilities;
 using StardewValley;
@@ -489,8 +490,8 @@ namespace StardewModdingAPI.Framework
         private RemoteContextModel? ReadContext(BinaryReader reader)
         {
             string data = reader.ReadString();
-            RemoteContextModel model = this.JsonHelper.Deserialize<RemoteContextModel>(data);
+            RemoteContextModel? model = this.JsonHelper.Deserialize<RemoteContextModel>(data);
-            return model.ApiVersion != null
+            return model?.ApiVersion != null
                 ? model
                 : null; // no data available for vanilla players
         }
@@ -499,13 +500,31 @@ namespace StardewModdingAPI.Framework
         /// <param name="message">The raw message to parse.</param>
         private void ReceiveModMessage(IncomingMessage message)
         {
-            // parse message
+            // read message JSON
             string json = message.Reader.ReadString();
-            ModMessageModel model = this.JsonHelper.Deserialize<ModMessageModel>(json);
-            HashSet<long> playerIDs = new HashSet<long>(model.ToPlayerIDs ?? this.GetKnownPlayerIDs());
             if (this.LogNetworkTraffic)
                 this.Monitor.Log($"Received message: {json}.");
 
+            // deserialize model
+            ModMessageModel? model;
+            try
+            {
+                model = this.JsonHelper.Deserialize<ModMessageModel>(json);
+                if (model is null)
+                {
+                    this.Monitor.Log($"Received invalid mod message from {message.FarmerID}.\nRaw message data: {json}");
+                    return;
+                }
+            }
+            catch (Exception ex)
+            {
+                this.Monitor.Log($"Received invalid mod message from {message.FarmerID}.\nRaw message data: {json}\nError details: {ex.GetLogSummary()}");
+                return;
+            }
+
+            // get player IDs
+            HashSet<long> playerIDs = new HashSet<long>(model.ToPlayerIDs ?? this.GetKnownPlayerIDs());
+
             // notify local mods
             if (playerIDs.Contains(Game1.player.UniqueMultiplayerID))
                 this.OnModMessageReceived(model);