Merge pull request #1568 from EPPlusSoftware/bug/issue1566

Fixes issue 1566

Author: OssianEPPlus

src/EPPlus/FormulaParsing/DependencyChain/RpnFormulaExecution.cs

@@ -474,7 +474,7 @@ private static object AddChainForFormula(RpnOptimizedDependencyChain depChain, R
                     if (depChain.processedCells.Contains(ExcelCellBase.GetCellId(ws?.IndexInList??ushort.MaxValue, address.FromRow, address.FromCol)) == false)
                     {
                         rd?.Merge(address.FromRow, address.FromCol);
-                        if (ws._formulas.Exists(address.FromRow, address.FromCol, ref v))
+                        if (ws._formulas.Exists(address.FromRow, address.FromCol, ref v) && v != null)
                         {
                             depChain._formulaStack.Push(f);
                             GetFormula(depChain, ws, address.FromRow, address.FromCol, v, ref f);

src/EPPlusTest/Issues/FormulaCalculationIssues.cs

@@ -419,5 +419,31 @@ public void i1540()
                 SaveAndCleanup(p);
 			}
 		}
-	}
+        [TestMethod]
+        public void i1566()
+        {
+            using (var package = new ExcelPackage())
+            {
+                var ws = package.Workbook.Worksheets.Add("Sheet1");
+                /* 
+                This reference to a custom function is a simulation of my use-case.
+                It doesn't appear to matter what the formula is, it just has to be set to something
+                ws.Cells["A3"].Formula = "1"; // this works just as well as "@SomeCustomVbaFunction(A1,A2)"
+                */
+                ws.Cells["A3"].Formula = "@SomeCustomVbaFunction(A1,A2)";
+                /* 
+                 * clear the formulas so that EPPlus doesn't go looking for SomeCustomVbaFunction
+                 I have purposefully chosen not to implement this function as a class extending ExcelFunction                
+                */
+                ws.Cells["A3"].ClearFormulas();
+                //ws.Cells["A3"].Formula = "0"; //This may be a workaround for now
+                ws.Cells["A3"].Value = "2000";
+                ws.Cells["A4"].Formula = "ROUNDUP(A3/1609.334,0)";
+
+                ws.Calculate();
+                Assert.AreEqual(2D, ws.Cells["A4"].Value);
+
+            }
+        }
+    }
 }