String isnullorEmpty gegen isnullorwhITespace

/* IsNullOrWhiteSpace is a convenience method that is similar to 
the following code, except that it offers superior performance: */

return String.IsNullOrEmpty(value) || value.Trim().Length == 0;

/* White-space characters are defined by the Unicode standard. 
The IsNullOrWhiteSpace method interprets any character that returns
a value of true when it is passed to the Char.IsWhiteSpace method as
a white-space character. */
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