Dynamic lambda expression for where clause

I'm filtering things from a dynamic list of objects using a lambda expression where clause. Consider, for instance, that it has three properties: foo, bar, and baz.

class item // let this be current class in dynamic item list
{
    bool foo;
    string bar;
    string baz;
}

Now, I can use the following expression to filter out items in a list when foo is false.

var filtered = itemList.Where("!foo");

I can even use strings values to filter the list.

var filtered = itemList.Where("bar==\"value\""); \\all items with bar = value

I want to determine if a list item's string value is not null or white space and instead has a certain value. I tried the code below

var filtered = itemList.Where("!String.IsNullOrWhiteSpace(baz)");

It made a mistake.

Expression of type 'System.Func`2[DynamicType,System.Object]' cannot be used for parameter of type 'System.String' of method 'Boolean IsNullOrWhiteSpace(System.String)'

Even though I was able to obtain a response from the following query

var filtered = itemList.Where("baz!=null && baz!=\"\"");

I was curious to know if there was a method I could utilizeString.IsNullOrWhiteSpace() in this case.