isNullOrWhiteSpace

IsNullOrWhiteSpace is a static method in the .NET framework and .NET Core class System.String. It determines whether a given string is null, empty, or consists solely of white-space characters.

The method returns a boolean value. It returns true if the input string is null, if its length is zero, or if every character in the string is classified as white space by Char.IsWhiteSpace. It returns false for any string that contains at least one non-whitespace character. White-space includes spaces, tabs, newlines, and other Unicode whitespace characters.

This method is commonly used to validate input before processing to avoid null reference errors or to treat blank input as missing. It is more comprehensive than a simple null-or-empty check because it also recognizes strings that appear blank due to whitespace only.

Difference from related checks: String.IsNullOrWhiteSpace differs from String.IsNullOrEmpty, which returns true only for null or empty strings and does not consider whitespace-only strings as empty. In contrast, IsNullOrWhiteSpace treats whitespace-only strings as effectively empty.

Usage examples: String.IsNullOrWhiteSpace(null) yields true; String.IsNullOrWhiteSpace(" ") yields true; String.IsNullOrWhiteSpace("text") yields false.

Notes: The method relies on Unicode-based whitespace definitions via Char.IsWhiteSpace, making it culture-insensitive. It was introduced with the .NET Framework 4.0 and is available in .NET Core and later runtimes. See also String.IsNullOrEmpty and Char.IsWhiteSpace for related checks.