$>g__Test1|0_0(List<string> strs) { if (strs != null && strs.Count == 1) { return strs[0]; } return string.Join(",", strs); }</code> Note that it returns the first element <i>without checking it for <c>null</c></i>. If you change the <c>var</c> to <c>string</c>, which, as noted above, is redundant, then the generated code includes a null-check. <code>string Test2(List<string> strs) { if(strs is [string s]) { return s; } return string.Join(",", strs); }</code> This is the generated code for the example above. <code>internal static string

$>g__Test2|0_1(List<string> strs) { if (strs != null && strs.Count == 1) { string text = strs[0]; if (text != null) { return text; } } return string.Join(",", strs); }</code> If you instead use <c>{ }</c> to indicate that you want to match a non-null object, then you also get the null-check. <code>string Test3(List<string> strs) { if(strs is [{} s]) { return s; } return string.Join(",", strs); }</code> This is the generated code for the example above. It is the same as the second example that uses <c>string</c> for the matched parameter. <code>internal static string

$>g__Test3|0_2(List<string> strs) { if (strs != null && strs.Count == 1) { string text = strs[0]; if (text != null) { return text; } } return string.Join(",", strs); }</code>