Enable NetworkCheckerHandler to use updated String methods

src/main/java/net/minecraftforge/fml/common/network/NetworkCheckHandler.java

@@ -28,8 +28,10 @@
 
 /**
  * A method annotated with this will be called when a remote network connection is offered.
- * The method should have two parameters, of types Map<String,String> and {@link Side}. It should return a boolean
- * true indicating that the remote party is acceptable, or false if not.
+ * The method should have two parameters, of types Map<String,String> and {@link Side}. It should return 
+ * a boolean true indicating that the remote party is acceptable, or false if not
+ * or a String null indicating that the remote party is acceptable, or notnull if not
+ * 
  *
  * <p>
  * When the method is invoked, the map will contain String keys and values listing all mods and their versions present.
@@ -38,6 +40,8 @@
  * <p>
  * This method will be invoked both when querying the status of the remote server, and when connecting to the remote server.
  *
+ * 
+ * 
  * <p>
  * <strong>NOTE: the server will not be setup at any point when this method is called. Do not try and interact with the server
  * or the client in any way, except to accept or reject the list of mods.</strong>

src/main/java/net/minecraftforge/fml/common/network/internal/NetworkModHolder.java

@@ -46,7 +46,7 @@ public class NetworkModHolder
     /**
      * Validates that the mods versions on the client and server are compatible with mod.
      */
-    public abstract class NetworkChecker {
+    public static abstract class NetworkChecker {
         /**
          * @deprecated use {@link #checkCompatible(Map, Side)}
          */
@@ -66,7 +66,7 @@ public String checkCompatible(Map<String,String> remoteVersions, Side side)
         }
     }
 
-    private class IgnoredChecker extends NetworkChecker {
+    private static class IgnoredChecker extends NetworkChecker {
         @Override
         public boolean check(Map<String, String> remoteVersions, Side side)
         {
@@ -151,12 +151,14 @@ public String checkCompatible(Map<String, String> remoteVersions, Side side)
         {
             try
             {
-                Boolean result = (Boolean) checkHandler.invoke(container.getMod(), remoteVersions, side);
-                if (result != null && result)
-                {
-                    return null;
+                if (checkHandler.getReturnType() == String.class) {
+                    return (String) checkHandler.invoke(container.getMod(), remoteVersions, side);
+                } else {
+                    Boolean result = (Boolean) checkHandler.invoke(container.getMod(), remoteVersions, side);
+                    if (result != null && result) {
+                        return null;
+                    } else return String.format("Failed mod's custom NetworkCheckHandler %s", container);
                 }
-                return String.format("Failed mod's custom NetworkCheckHandler %s", container);
             }
             catch (Exception e)
             {
@@ -171,6 +173,7 @@ public String toString()
             return String.format("Invoking method %s", checkHandler.getName());
         }
     }
+
     private static int assignedIds = 1;
 
     private int localId;