Add LeaveOnlyNotNone() method in the parent class

sources/Data/Collections/ArrayListIterator.uc

@@ -41,9 +41,10 @@ public function bool Initialize(Collection relevantArray)
     return true;
 }
 
-public function LeaveOnlyNotNone()
+public function Iter LeaveOnlyNotNone()
 {
     skipNoneReferences = true;
+    return self;
 }
 
 public function Iter Next(optional bool deprecated)

sources/Data/Collections/HashTableIterator.uc

@@ -51,9 +51,10 @@ public function bool Initialize(Collection relevantArray)
     return true;
 }
 
-public function LeaveOnlyNotNone()
+public function Iter LeaveOnlyNotNone()
 {
     skipNoneReferences = true;
+    return self;
 }
 
 public function Iter Next(optional bool deprecated)

sources/Data/Collections/Iter.uc

@@ -86,6 +86,13 @@ public function AcediaObject GetKey();
  */
 public function bool HasFinished();
 
+/**
+ *  Makes caller iterator skip any `none` items during iteration.
+ *
+ *  @return Reference to caller `Iterator` to allow for method chaining.
+ */
+public function Iter LeaveOnlyNotNone();
+
 defaultproperties
 {
 }