Fix: Handle nullable fallback for optional parameter parsing

Ensure the fallback value is properly checked for null before usage. This prevents potential issues when the initializer value is not defined, improving robustness in parameter parsing.

Author: AnnaSasDev

src/CodeOfChaos.CliArgsParser.Generators/ParameterDto.cs

@@ -54,11 +54,13 @@ public string GetWithPropertyDictionary() {
 
         if (PropertyType == "bool") return $"parameterDictionary.GetOptionalParameterByPossibleNames<{PropertyType}>({Name}, {ShortName})";
 
-        string fallback = Symbol.DeclaringSyntaxReferences
+        string? fallback = Symbol.DeclaringSyntaxReferences
             .Select(r => r.GetSyntax())
             .OfType<PropertyDeclarationSyntax>()
-            .FirstOrDefault()?.Initializer?.Value.ToString() ?? "default";
-
-        return $"parameterDictionary.GetOptionalParameterByPossibleNames<{PropertyType}>({Name}, {ShortName}) ?? {fallback}";
+            .FirstOrDefault()?.Initializer?.Value.ToString();
+        
+        // ReSharper disable once ConvertIfStatementToReturnStatement
+        if (fallback is null) return $"parameterDictionary.GetOptionalParameterByPossibleNames<{PropertyType}>({Name}, {ShortName})";
+        return $"parameterDictionary.GetOptionalParameterByPossibleNames<{PropertyType}?>({Name}, {ShortName}) ?? {fallback}";
     }
 }