Extension method to add a get property that returns a default value (extends the CodeTypeDeclaration type).

CodeDomExtensionAddDefaultGetter.cs

public static class CodeDomExtensionMethods {
	/// <summary>
	/// Adds a get property that returns a default value.
	/// </summary>
	/// <param name="type"></param>
	/// <param name="typeName"></param>
	/// <param name="propertyName"></param>
	/// <param name="attrs"></param>
	/// <returns></returns>
	public static CodeMemberProperty AddDefaultGetter(this CodeTypeDeclaration type, string typeName,
		string propertyName, MemberAttributes attrs = MemberAttributes.Public)
	{
		if (typeName == null) throw new ArgumentNullException(nameof(typeName));

		var tokenBaseType = new CodeTypeReference(new CodeTypeParameter(typeName));

		if (typeName == "string" || typeName == "System.String")
		tokenBaseType = new CodeTypeReference(typeof(string));

		var defaultProperty = new CodeMemberProperty {
			Type = tokenBaseType,
			Name = propertyName,
			Attributes = attrs,
			HasGet = true
		};

		if (!attrs.HasFlag(MemberAttributes.Abstract)) {
			defaultProperty.GetStatements.Add(new CodeMethodReturnStatement {
				Expression = new CodeDefaultValueExpression {
					Type = tokenBaseType
				}
			});
		}

		type.Members.Add(defaultProperty);

		return defaultProperty;
	}
}