private System.String ExpandWorkOrderVariables( System.String @string ) {
    @string = @string.TrimToNull();
    if ( System.String.IsNullOrEmpty( @string ) ) {
        return null;
    }
    foreach ( var @var in ( this.Variables ?? new Variable[ 0 ] ) ) {
        @string = @string.Replace( "%var:" + @var.Name + "%", @var.Value ?? System.String.Empty );
    }
    return @string;
}