if (decimal.TryParse(numberBuilder.ToString(), out var number))
{
if (number < minRange || number > maxRange)
{
cleanGenerator = true;
}
var can't be a variable since it's a keyword and number not declared.
In release this may be okay, but source has this in it.
ClassUtility.cs
You don't know bases,
var can be used for declare almost every types of variable in Implicitly typed. So it's work without problem

Also for be able to declare a variable inside a tryparse, this expression is presented since C# 6.0, available since C#7.0 so it's a bit old.. C# 6.0 features explained on this article:
https://www.c-sharpcorner.com/article/getting-started-with-c-sharp-6-0-new-features/ (Article written in 2016..) And C# 6.0 has been released in 2015, a more detailed article:
https://www.dotnetcurry.com/csharp/1465/csharp-evolutionAlso for be sure, you can install Visual Studio 2017 or a higher version for be able to support almost every C# version code.
Visual Studio 2015 can support it too, but you have to install yourself the support, with various techniques, you can also use tools who help in coding like ReSharper, who provide the ability to support this expression and other expressions for compile the source code.
Now go to learn C# and return back, or you can make some research by yourself before to tell something.
Have a nice day.