Move TriState converter

api/src/main/java/com/velocitypowered/api/permission/PermissionSubject.java

@@ -39,17 +39,6 @@ public interface PermissionSubject {
    * @return subject's permission checker
    */
   default PermissionChecker getPermissionChecker() {
-    return permission -> {
-      final Tristate state = getPermissionValue(permission);
-      if (state == Tristate.TRUE) {
-        return TriState.TRUE;
-      } else if (state == Tristate.UNDEFINED) {
-        return TriState.NOT_SET;
-      } else if (state == Tristate.FALSE) {
-        return TriState.FALSE;
-      } else {
-        throw new IllegalArgumentException();
-      }
-    };
+    return permission -> getPermissionValue(permission).toAdventureTriState();
   }
 }

api/src/main/java/com/velocitypowered/api/permission/Tristate.java

@@ -7,6 +7,7 @@
 
 package com.velocitypowered.api.permission;
 
+import net.kyori.adventure.util.TriState;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
@@ -81,4 +82,16 @@ public enum Tristate {
   public boolean asBoolean() {
     return this.booleanValue;
   }
+
+  public TriState toAdventureTriState() {
+    if (this == Tristate.TRUE) {
+      return TriState.TRUE;
+    } else if (this == Tristate.UNDEFINED) {
+      return TriState.NOT_SET;
+    } else if (this == Tristate.FALSE) {
+      return TriState.FALSE;
+    } else {
+      throw new IllegalArgumentException();
+    }
+  }
 }