Convert a String to any Type as Nullable

Often when working with objects like the DataRow it is necessary to check for DbNull.Value. Here is a generic method that will accept a string representing any type, along with the type desired, and it will convert to the required value or null.

/// <summary>
        /// Convert a string to any type as nullable
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="valueAsString">string value</param>
        /// <returns>Nullable instance of coverted value</returns>
        public static T? GetValueOrNull<T>( string valueAsString )
    where T : struct
        {
            if (string.IsNullOrEmpty(valueAsString))
                return null;
            return (T)Convert.ChangeType(valueAsString, typeof(T));
        }

Usage:
cd.DocumentID = GetValueOrNull<long>(row["i_document_id"].ToString());

You can also easily turn this into an extension method on the String type:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MyProject
{

    public static class MyProjectExtensions
    {
         /// <summary>
        /// Convert a string to any type as nullable
        /// </summary>
        /// <typeparam name="T">Type</typeparam>
        /// <param name="valueAsString">string value</param>
        /// <returns>Nullable instance of coverted value</returns>
        public static T? GetValueOrNull<T>( this string valueAsString )
    where T : struct
        {
             if (string.IsNullOrEmpty(valueAsString))
                 return null;
            return (T)Convert.ChangeType(valueAsString, typeof(T));
        }
    }  
}

usage:
var cd = new Thing();
cd.Amount = row["amount"].ToString().GetValueOrNull<decimal>();

An alternative that avoids the need to call ToString() on the object to process is to use type Object:

public static T? GetValueOrNull<T>(this object candidate) where T : struct
        {
             if (candidate == DBNull.Value)
                 return null;
            return (T)Convert.ChangeType(candidate, typeof(T));
        }

The above would be especially useful when processing DataRow Items, which are always type Object.