Attempted itemstack json serialization fixes

Signed-off-by: Irmo van den Berge <irmo.vandenberge@ziggo.nl>

src/main/java/com/bergerkiller/bukkit/common/config/JsonSerializer.java

@@ -1,8 +1,10 @@
 package com.bergerkiller.bukkit.common.config;
 
+import java.util.Collections;
 import java.util.Map;
 
 import com.bergerkiller.bukkit.common.config.yaml.YamlDeserializer;
+import com.bergerkiller.bukkit.common.map.gson.EmptyMapSerializer;
 import com.google.gson.GsonBuilder;
 import org.bukkit.inventory.ItemStack;
 
@@ -14,7 +16,9 @@ import com.bergerkiller.bukkit.common.utils.LogicUtil;
  * Can serialize and deserialize various objects from/to a JSON String.
  */
 public class JsonSerializer {
-    private final com.google.gson.Gson gson = new GsonBuilder().disableHtmlEscaping().create();
+    private final com.google.gson.Gson gson = new GsonBuilder().disableHtmlEscaping()
+            .registerTypeAdapter(Collections.emptyMap().getClass(), new EmptyMapSerializer())
+            .create();
 
     public ItemStack fromJsonToItemStack(String json) throws JsonSyntaxException {
         Map<String, Object> mapping = jsonToMap(json);

src/main/java/com/bergerkiller/bukkit/common/map/gson/EmptyMapSerializer.java

@@ -0,0 +1,17 @@
+package com.bergerkiller.bukkit.common.map.gson;
+
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonSerializationContext;
+import com.google.gson.JsonSerializer;
+
+import java.lang.reflect.Type;
+import java.util.Map;
+
+public class EmptyMapSerializer implements JsonSerializer<Map<?, ?>> {
+
+    @Override
+    public JsonElement serialize(Map<?, ?> o, Type type, JsonSerializationContext jsonSerializationContext) {
+        return new JsonObject();
+    }
+}

src/main/java/com/bergerkiller/bukkit/common/utils/LogicUtil.java

@@ -1183,17 +1183,22 @@ public class LogicUtil {
             }
         }
 
+        boolean cloned = false;
         for (Map.Entry<String, Object> entry : values.entrySet()) {
             Object value = entry.getValue();
             if (value instanceof ConfigurationSerializable) {
                 Map<String, Object> serialized = serializeDeep((ConfigurationSerializable) value);
-                try {
-                    entry.setValue(serialized);
-                } catch (UnsupportedOperationException ex) {
-                    // This shouldn't ever be hit, but kept it for safety
+                if (!cloned) {
+                    try {
+                        entry.setValue(serialized);
+                        continue;
+                    } catch (UnsupportedOperationException ex) { /* Shouldn't happen but just in case */ }
+
                     values = new LinkedHashMap<>(values);
-                    values.put(entry.getKey(), serialized);
+                    cloned = true;
                 }
+
+                values.put(entry.getKey(), serialized);
             }
         }
         return values;

src/test/java/com/bergerkiller/bukkit/common/JsonSerializerTest.java

@@ -9,6 +9,8 @@ import com.bergerkiller.generated.com.mojang.authlib.properties.PropertyHandle;
 import com.bergerkiller.generated.org.bukkit.craftbukkit.util.CraftMagicNumbersHandle;
 import org.junit.Test;
 
+import java.util.Collections;
+import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.UUID;
 
@@ -17,6 +19,15 @@ import static org.junit.Assert.*;
 public class JsonSerializerTest {
     final int dataVersion = CraftMagicNumbersHandle.getDataVersion();
 
+    @Test
+    public void testEmptyMapToJson() {
+        JsonSerializer serializer = new JsonSerializer();
+        Map<String, Object> jsonMap = new LinkedHashMap<>();
+        jsonMap.put("key", Collections.emptyMap());
+        String json = serializer.toJson(jsonMap);
+        assertEquals("{\"key\":{}}", json);
+    }
+
     @Test
     public void testItemStackToJsonStick() throws JsonSerializer.JsonSyntaxException {
         JsonSerializer serializer = new JsonSerializer();