HOCON adapter: `ExpandKeys` errors when key length == 0

[Aaronontheweb]

Version Information
Version of Akka.NET? Akka.Hosting
Which Akka.NET Modules? at least v1.5.44, if not earlier

Describe the bug

Akka.Hosting/src/Akka.Hosting/Configuration/ConfigurationHoconAdapter.cs

Lines 40 to 70 in bbabe2a

	private static HoconValue ExpandKey(this IConfigurationSection config, HoconObject parent, bool normalizeKeys)
	{
	// Sanitize configuration brought in from environment variables,
	// "__" are already converted to ":" by the environment configuration provider.
	var sanitized = (normalizeKeys ? config.Key.ToLowerInvariant() : config.Key).Replace("_", "-");
	var keys = sanitized.SplitDottedPathHonouringQuotes().ToList();
	// No need to expand the chain
	if (keys.Count == 1)
	{
	return parent.GetOrCreateKey(keys[0]);
	}
	var currentObj = parent;
	while (keys.Count > 1)
	{
	var key = keys.Pop();
	var currentValue = currentObj.GetOrCreateKey(key);
	if (currentValue.IsObject())
	{
	currentObj = currentValue.GetObject();
	}
	else
	{
	currentObj = new HoconObject();
	currentValue.AppendValue(currentObj);
	}
	}
	return currentObj.GetOrCreateKey(keys[0]);
	}

If keys.length == 0, that scenario is unhandled inside this method and we try to access keys[0], which results in an IndexOutOfRange exception.

This behavior appears to be dependent on the types of environment variables that are present - in my case, it's these ones:

Expected behavior

Parser should not die on IConfigurationSection instances that have no key / path.

Actual behavior

Throws an IndexOutOfRange exception currently.

[Arkatufus]

I'm pretty sure this is caused by a "bug" in Microsoft.Extensions.Configuration.EnvironmentVariables, configuration section name/key should always have a value, but if the environment variable is named __MISE_SESSION, the library would just eat the double underscore, treat it as a dot, and create a configuration section with an empty name/key.

Would also need to check to see if if does the same with quadruple underscore.