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Few months ago I posted my code Getting a single value from the DB. I implemented suggested changes and this is how it looks like right now:

public class DataBase : Page
{
 
 protected static readonly ILog log = LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
 protected static string ConnectionString;
 public DataBase()
 {
 ConnectionString = GetConnectionString();
 }
 public static String GetConnectionString()
 {
 return ConfigurationManager.ConnectionStrings["abc"].ConnectionString;
 }
 public static T GetValue<T>(string query)
 where T : IComparable, IConvertible, IEquatable<T>
 {
 Object value = GetValue(query);
 if (Convert.IsDBNull(value))
 return GetDefaultValue<T>();
 return (T)Convert.ChangeType(value, typeof(T));
 }
 public static T GetDefaultValue<T>()
 where T : IComparable, IConvertible, IEquatable<T>
 {
 if (typeof(T) == typeof(String))
 return (T)(object)String.Empty;
 return default(T);
 }
private static Object GetValue(string query)
 {
 try
 {
 using (SqlConnection connection = new SqlConnection(ConnectionString))
 using (SqlCommand command = new SqlCommand(query, connection))
 {
 connection.Open();
 return command.ExecuteScalar();
 }
 }
 catch (Exception e)
 {
 LogQueryError(query, e);
 return DBNull.Value;
 }
 }
protected static void LogQueryError(string query, Exception e)
 {
 log.Error(string.Format("Error while executing Query ({0}): {1}", query, e.Message));
 }
}

One explanation. The purpose of where T : IComparable, IConvertible, IEquatable<T> is to have single method for value types and strings. (inspired by C# Generic constraints to include value types AND strings

What do you think about this piece of code?