Prefix spaces for each line in a string

My code generator requires to generate code with right indentation, so I need to prefix spaces for each line of a string. After google the world, there isn’t a out-of-box solution for me to use, finally I came up with my own solution:

internal static string Indent(this string content, int level = 1) =>
    string.Join(Environment.NewLine, content
        .Split(new[] { "\r\n" }, StringSplitOptions.None)
        .Select(_ => $"{(_ == string.Empty ? string.Empty : new string(' ', level * 4))}{_}")

Usage like this:

var result = str.Indent();