diff --git a/source/Trek-12/Models/Rules/Rules.cs b/source/Trek-12/Models/Rules/Rules.cs
index 8a7dc43..73d4467 100644
--- a/source/Trek-12/Models/Rules/Rules.cs
+++ b/source/Trek-12/Models/Rules/Rules.cs
@@ -174,6 +174,8 @@ 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)
             {