Added ListUtils#toSingletonList

eco-api/src/main/java/com/willfp/eco/util/ListUtils.java

@@ -1,8 +1,10 @@
 package com.willfp.eco.util;
 
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -55,6 +57,22 @@ public final class ListUtils {
         return frequencyMap;
     }
 
+    /**
+     * Convert nullable object to either singleton list or empty list.
+     *
+     * @param object The object.
+     * @param <T>    The type of the object.
+     * @return The list.
+     */
+    @NotNull
+    public static <T> List<T> toSingletonList(@Nullable final T object) {
+        if (object == null) {
+            return Collections.emptyList();
+        } else {
+            return Collections.singletonList(object);
+        }
+    }
+
     private ListUtils() {
         throw new UnsupportedOperationException("This is a utility class and cannot be instantiated");
     }