feat: add HasOwner PlotFilter filter (#4259)

* feat: add HasOwner PlotFilter filter
 - closes #3831

* change since to TODO

* Address feedback

---------

Co-authored-by: Alexander Brandes <mc.cache@web.de>

Core/src/main/java/com/plotsquared/core/util/query/HasOwnerFilter.java

@@ -0,0 +1,31 @@
+/*
+ * PlotSquared, a land and world management plugin for Minecraft.
+ * Copyright (C) IntellectualSites <https://intellectualsites.com>
+ * Copyright (C) IntellectualSites team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.plotsquared.core.util.query;
+
+import com.plotsquared.core.plot.Plot;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+class HasOwnerFilter implements PlotFilter {
+
+    @Override
+    public boolean accepts(final @NonNull Plot plot) {
+        return plot.hasOwner();
+    }
+
+}

Core/src/main/java/com/plotsquared/core/util/query/PlotQuery.java

@@ -219,6 +219,16 @@ public final class PlotQuery implements Iterable<Plot> {
         return this.addFilter(new OwnersIncludeFilter(owner.getUUID()));
     }
 
+    /**
+     * Query only for plots that have an owner
+     *
+     * @return The query instance
+     * @since TODO
+     */
+
+    public @NonNull PlotQuery hasOwner() {
+        return this.addFilter(new HasOwnerFilter());
+    }
     /**
      * Query for plots with a specific alias
      *