diff --git a/source/Trek-12/Models/Rules/Rules.cs b/source/Trek-12/Models/Rules/Rules.cs
index bd8c8cf..6fa645a 100644
--- a/source/Trek-12/Models/Rules/Rules.cs
+++ b/source/Trek-12/Models/Rules/Rules.cs
@@ -209,6 +209,8 @@ namespace Models.Rules
         public List<Cell> EveryAdjacentCells(Cell choosenCell, List<Cell> cells)
         {
             List<Cell> adjacentCells = new List<Cell>();
+            
+            if (choosenCell == null || cells == null) return adjacentCells;
 
             foreach (var cell in cells)
             {