Warn about null permission functions.

proxy/src/main/java/com/velocitypowered/proxy/connection/client/LoginSessionHandler.java

@@ -17,6 +17,7 @@ import com.velocitypowered.api.event.connection.PreLoginEvent.PreLoginComponentR
 import com.velocitypowered.api.event.permission.PermissionsSetupEvent;
 import com.velocitypowered.api.event.player.GameProfileRequestEvent;
 import com.velocitypowered.api.event.player.PlayerChooseInitialServerEvent;
+import com.velocitypowered.api.permission.PermissionFunction;
 import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.util.GameProfile;
 import com.velocitypowered.api.util.UuidUtils;
@@ -231,7 +232,16 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
           .thenAcceptAsync(event -> {
             if (!mcConnection.isClosed()) {
               // wait for permissions to load, then set the players permission function
-              player.setPermissionFunction(event.createFunction(player));
+              final PermissionFunction function = event.createFunction(player);
+              if (function == null) {
+                logger.error(
+                    "A plugin permission provider {} provided an invalid permission function"
+                        + " for player {}. This is a bug in the plugin, not in Velocity. Falling"
+                        + " back to the default permission function.", player.getUsername(),
+                    event.getProvider());
+              } else {
+                player.setPermissionFunction(function);
+              }
               completeLoginProtocolPhaseAndInitialize(player);
             }
           }, mcConnection.eventLoop());

proxy/src/main/java/com/velocitypowered/proxy/console/VelocityConsole.java

@@ -65,6 +65,13 @@ public final class VelocityConsole extends SimpleTerminalConsole implements Cons
     PermissionsSetupEvent event = new PermissionsSetupEvent(this, s -> ALWAYS_TRUE);
     // we can safely block here, this is before any listeners fire
     this.permissionFunction = this.server.getEventManager().fire(event).join().createFunction(this);
+    if (this.permissionFunction == null) {
+      logger.error(
+          "A plugin permission provider {} provided an invalid permission function"
+              + " for the console. This is a bug in the plugin, not in Velocity. Falling"
+              + " back to the default permission function.", event.getProvider());
+      this.permissionFunction = ALWAYS_TRUE;
+    }
   }
 
   @Override