Syntactic sugar to be able to require something to be true, otherwise throws and exception of your choosing.
This is also known as a guard clause.
Mandate.That<TException>(<bool expression>, "Optional Custom exception message goes in here.");
Mandate.IsNotNull<TException>(object, "Optional Custom exception message goes in here.");
var someVar = -1;
Mandate.That<InvalidOperationException>(someVar > 0, $"{someVar} must be greater than zero!"); //throws an InvalidOperationException
//we'll never get here
var someVar = 1;
Mandate.That<InvalidOperationException>(someVar > 0, $"{someVar} must be greater than zero!"); //will not throw
//more code that will execute
decimal? someVar = null;
Mandate.That<InvalidOperationException>(someVar != null, $"{someVar} must not be null!"); //will throw
//we won't get here
decimal? someVar = null;
Mandate.IsNotNull<InvalidOperationException>(someVar, $"{someVar} was null!"); //will throw
//we won't get here