Unichar and text bug

src/EPPlus/FormulaParsing/Excel/Functions/Text/Text.cs

@@ -47,9 +47,9 @@ public class Text : ExcelFunction
         public override CompileResult Execute(IList<FunctionArgument> arguments, ParsingContext context)
         {
             var value = arguments[0].ValueFirst;
-            var format = ArgToString(arguments, 1);
+            var format = ArgToString(arguments, 1) ?? "";
             var invariantFormat = GetInvariantFormat(format);
-
+            
             var result = context.ExcelDataProvider.GetFormat(value, invariantFormat, out bool isValidFormat);
             if(!isValidFormat)
             {
@@ -61,6 +61,10 @@ public override CompileResult Execute(IList<FunctionArgument> arguments, Parsing
 
         private static string GetInvariantFormat(string format)
         {
+            if (string.IsNullOrEmpty(format))
+            {
+                return format;
+            }
             var nds = CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator;
             var ds = nds[0];
             var ngs = CultureInfo.CurrentCulture.NumberFormat.NumberGroupSeparator;

src/EPPlus/FormulaParsing/Excel/Functions/Text/Unichar.cs

@@ -35,7 +35,7 @@ public override CompileResult Execute(IList<FunctionArgument> arguments, Parsing
                 &&
                 short.TryParse(ArgToString(arguments, 0), out short arg))
             {
-                return CreateResult(char.ConvertFromUtf32(arg), DataType.Integer);
+                return CreateResult(char.ConvertFromUtf32(arg).ToString(), DataType.String);
             }
             return CreateResult(ExcelErrorValue.Values.Value, DataType.ExcelError);
         }

src/EPPlusTest/FormulaParsing/Excel/Functions/TextFunctionsTests.cs

@@ -307,6 +307,22 @@ public void UnicharShouldReturnCorrectChar()
             Assert.AreEqual("a", result.Result);
         }
 
+        [TestMethod]
+        public void UnicharShouldReturnCorrectResultNumeric()
+        {
+            using (var package = new ExcelPackage())
+            {
+                var sheet = package.Workbook.Worksheets.Add("test");
+                sheet.Cells["A1"].Value = 178;
+
+                sheet.Cells["B2"].Formula = "UNICHAR(A1)";
+                sheet.Calculate();
+
+                var result = sheet.Cells["B2"].Value;
+                Assert.AreEqual("²", result);
+            }
+        }
+
         [TestMethod]
         public void NumberValueWithEmptyStringShouldReturn0()
         {

src/EPPlusTest/Issues/FormulaCalculationIssues.cs

@@ -1347,6 +1347,15 @@ public void s968()
             Assert.AreEqual("One or more errors occurred during the valuation run", ws.Cells["E40"].Value);
             Assert.IsNull(ws.Cells["D41"].Value);
         }
+
+
+        [TestMethod]
+        public void s973()
+        {
+            using var package = OpenTemplatePackage("s973.xlsx");
+            package.Workbook.Calculate();
+            Assert.AreEqual("12,35²", package.Workbook.Worksheets[0].Cells["A3"].Value);
+        }
     }
 }