In your case I suggest that you would create a class with the fields that represent that XML and use DataAnnotations for properties that can not be empty, would be the Required attribute, see:

[Required(ErrorMessage = "Nome é obrigatório.")]
public string Nome {get; set;}

It is a good alternative for validating objects, you can even implement the IValidatableObject interface on the object to be validated.

Using a list

If you want to check multiple values at once, you can use a list for this:

var valores = new List<string>{ "Hi", "casa", "Teste", "ga", "     sa ", null}; 

In the Exists method you specify the predicate with the condition, which would be:

v => string.IsNullOrWhiteSpace(v)

To check if there are any nulls in the range of values null , empty "" or whitespace " " .

See the complete code:

using static System.Console;
using System.Collections.Generic;

public class Program
{
    public static void Main()
    {               
        var valores = new List<string>{ "Hi", "casa", "Teste", "ga", "     sa ", null}; 
        var algumElementoVazioOuNulo = valores.Exists(v => string.IsNullOrWhiteSpace(v));
        if (algumElementoVazioOuNulo)
        {
            WriteLine("Sim");   
        }               
        else 
        {
            WriteLine("Nao");
        }
    }
}

See working at .NET Fiddle .

Learn more at documentation .

You can use the & & (e) or || (or) , but you still have to do the individual verification of each item. You can try something like:

if(val1 != "" && val2 != "" && val3 != ""){ ... }

Dai just follow the truth table