API: Add Tristate#fromOptionalBoolean (#1125)

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2018-2022 Velocity Contributors
+ * Copyright (C) 2018-2023 Velocity Contributors
  *
  * The Velocity API is licensed under the terms of the MIT License. For more details,
  * reference the LICENSE file in the api top-level directory.
@@ -7,6 +7,7 @@
 
 package com.velocitypowered.api.permission;
 
+import java.util.Optional;
 import net.kyori.adventure.util.TriState;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -66,6 +67,21 @@ public enum Tristate {
     return val ? TRUE : FALSE;
   }
 
+  /**
+   * Returns a {@link Tristate} from an {@link Optional}.
+   *
+   * <p>Unlike {@link #fromBoolean(boolean)}, this method returns {@link #UNDEFINED}
+   * if the value is empty.</p>
+   *
+   * @param val the optional boolean value
+   * @return {@link #UNDEFINED}, {@link #TRUE} or {@link #FALSE}, if the value is empty,
+   *     <code>true</code> or <code>false</code>, respectively.
+   */
+  public static Tristate fromOptionalBoolean(Optional<Boolean> val) {
+    return val.map(Tristate::fromBoolean).orElse(UNDEFINED);
+  }
+
+
   private final boolean booleanValue;
 
   Tristate(boolean booleanValue) {