Add support to conditional check for undefined tags

Author: Brett Prucha

samples/docx/TestIfStatement.docx

@@ -526,7 +526,7 @@ private static void ReplaceStatements(OpenXmlElement xmlElement, Dictionary<stri
 
                 var statement = paragraphs[ifIndex].InnerText.Split(' ');
 
-                var tagValue = tags[statement[1]] ?? "NULL";
+                var tagValue = tags.ContainsKey(statement[1]) ? tags[statement[1]] ?? "NULL" : "{UNDEFINED}";
 
                 var checkStatement = statement.Length == 4 ? EvaluateStatement(tagValue.ToString(), statement[2], statement[3]) : !bool.Parse(tagValue.ToString());
 
@@ -557,6 +557,9 @@ private static string EvaluateIfStatement(string text)
                 var ifEndIndex = text.IndexOf(")if", ifIndex, StringComparison.Ordinal);
 
                 var statement = text.Substring(ifIndex + ifStartTag.Length, ifEndIndex - (ifIndex + ifStartTag.Length)).Split(',');
+
+                if(Regex.IsMatch(statement[0], "^{{.*}}$"))
+                    statement[0] = "{UNDEFINED}";
 
                 var checkStatement = EvaluateStatement(statement[0], statement[1], statement[2]);
 

src/MiniWord/MiniWord.Implment.cs

@@ -153,6 +153,8 @@ public void MiniWordIfStatement_FirstIf()
             Assert.Contains("Points are greater than 100", docXml);
             Assert.Contains("CreateDate is not less than 2021", docXml);
             Assert.DoesNotContain("CreateDate is not greater than 2021", docXml);
+            Assert.Contains("Foo is undefined", docXml);
+            Assert.Contains("Bar is undefined", docXml);
         }
 
         [Fact]