chore: Update README.md and suppress warning

Author: PhoenixVX

README.md

@@ -16,6 +16,8 @@ and your JAR file associations are properly configured.
 
 For more information, check out the [RetroMCP Wiki](https://github.com/MCPHackers/RetroMCP-Java/wiki).
 
+[![](https://dcbadge.limes.pink/api/server/https://discord.gg/8Qky5XY)](https://discord.gg/8Qky5XY)
+
 # Features
 
 * Automatically download Minecraft .jar and libraries from version JSONs

src/main/java/org/mcphackers/mcp/tools/mappings/MappingUtil.java

@@ -10,6 +10,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 
 import net.fabricmc.mappingio.MappingReader;
 import net.fabricmc.mappingio.MappingWriter;
@@ -124,7 +125,7 @@ public static void mergeMappings(Path client, Path out) throws IOException {
 
 		// Switch the namespaces from official -> named to named -> official
 		// Rename the namespaces from named -> official to named -> client
-		MappingNsRenamer nsRenamer = new MappingNsRenamer(MappingWriter.create(out, MappingFormat.TINY_2_FILE), nsRenames);
+		MappingNsRenamer nsRenamer = new MappingNsRenamer(Objects.requireNonNull(MappingWriter.create(out, MappingFormat.TINY_2_FILE)), nsRenames);
 		MappingSourceNsSwitch nsSwitch = new MappingSourceNsSwitch(nsRenamer, currentDst);
 		MappingReader.read(client, MappingFormat.TINY_2_FILE, nsSwitch);
 	}