String validation

Lately, I'm often faced to check if a given string is null, empty or only white space. You all know the built-in method string.IsNullOrEmpty(string). However when writting code, for me, it feels quite juddery to use a static type method to check that. So I decided to give an extension method so I can just write stringVariable.IsNullOrEmpty(). You may think: "How can you execute a member method on a null-reference?". This is possible, because all extended methods are technically seen, static methods - they just pretend to be member methods.

And when I do variable checks, I like to use the null-coalescing operator (the double question mark ??). However, this is not possible when the string is just empty or whitespace. To solve that, I wrote also some extended methods, so you can just use stringVariable.EmptyToNull() or stringVariable.WhiteSpaceToNull(). Both just straighten a given value to null, if it equals empty or white space.

using System;
using System.Globalization;
 
namespace Luegisdorf
{
    /// <summary>
    /// Provides extended functionality for instances of type string
    /// </summary>
    public static class StringExtensions
    {
        /// <inheritdoc cref="string.IsNullOrEmpty(string)"/>
        public static bool IsNullOrEmpty(this string value)
            => string.IsNullOrEmpty(value);
 
        /// <inheritdoc cref="string.IsNullOrWhiteSpace(string)"/>
        public static bool IsNullOrWhiteSpace(this string value)
            => string.IsNullOrWhiteSpace(value);
 
 
        /// <summary>
        /// Straights string to <c>null</c>, if given instance equals to empty string.
        /// </summary>
        /// <remarks>
        /// Can mostly used to null-straighten a string when using validation 
        /// with null-coalescing operator.
        /// </remarks>
        /// <param name="instance">
        /// The instance to straighten
        /// </param>
        /// <returns>
        /// <c>Null</c>, if the given <paramref>instance</paramref> is already <c>null</c> 
        /// or equals empty string, 
        /// otherwise the given <c>instance</c>.
        /// </returns>
        /// <example>
        /// Inline usage: 
        /// <code>
        /// var candidate = string.Empty;
        /// var length = (candidate.EmptyToNull() 
        ///     ?? throw new Exception("Candidate must contain value")).Length;
        /// </code>        
        /// 
        /// If condition usage: 
        /// <code>
        /// var candidate = string.Empty;
        /// if ((candidate.EmptyToNull() 
        ///     ?? throw new Exception("Candidate must contain value")) 
        ///         is string properString)
        /// {
        ///    var length = properString.Length;
        ///    var firstCharacter = properString[0];
        /// }
        /// </code>        
        /// </example>
        public static string EmptyToNull(this string instance)
        {
            string ret = instance;
 
            if (string.IsNullOrEmpty(instance))
            {
                ret = null;
            }
            return ret;
        }
 
        /// <summary>
        /// Straights string to <c>null</c>, if given instance equals to empty string.
        /// </summary>
        /// <remarks>
        /// Can mostly used to null-straighten a string when using validation 
        /// with null-coalescing operator.
        /// </remarks>
        /// <param name="instance">
        /// The instance to straighten
        /// </param>
        /// <returns>
        /// <c>Null</c>, if the given <paramref>instance</paramref> is already <c>null</c> 
        /// or equals white space, 
        /// otherwise the given <c>instance</c>.
        /// </returns>
        /// <example>
        /// Inline usage: 
        /// <code>
        /// var candidate = string.Empty;
        /// var length = (candidate.WhiteSpaceToNull() 
        ///     ?? throw new Exception("Candidate must contain value")).Length;
        /// </code>        
        /// 
        /// If condition usage: 
        /// <code>
        /// var candidate = string.Empty;
        /// if ((candidate.WhiteSpaceToNull() 
        ///     ?? throw new Exception("Candidate must contain value")) 
        ///         is string properString)
        /// {
        ///    var length = properString.Length;
        ///    var firstCharacter = properString[0];
        /// }
        /// </code>        
        /// </example>
        public static string WhiteSpaceToNull(this string instance)
        {
            string ret = instance;
 
            if (string.IsNullOrWhiteSpace(instance))
            {
                ret = null;
            }
            return ret;
        }
    }
}