Question

I have a method like this:

public string StartCapture(string[] args)
{
    if(args[0].Trim() == null || args[0].Trim() == string.Empty )
    {
        //do stuff
    }
}

Why I get a note that args[0].Trim() == null will always be false?

Answer 1

Trim() is not going to return null. The issue you might have is if args[0] is null, or args itself is null, but the result of Trim() will never be null, and therefore the comparison to null will always be false.

Trim Method

If the current string equals Empty or all the characters in the current instance consist of white-space characters, the method returns Empty.

You may want to simply check

 if (args == null || args.Length == 0 || string.IsNullOrWhiteSpace(args[0]))
 {
     // null or empty array or empty first element
 }