public ExpressionParser(Expression expression, ParameterExpression[] parameters = null, object[] parameterValues = null,
bool textOnly = false, int baseParamIndex = 0, Type testClass = null)
{
RootExpression = expression;
_parameters = parameters ?? new ParameterExpression[0];
_parameterValues = parameterValues ?? new object[0];
TestClass = testClass ?? GetTestClass();
TextOnly = textOnly;
_nextParamIndex = baseParamIndex;
}