Empty app config file throws exception on app load about meadow.core

[patridge]

If we put an exception handler on the ConfigurationBuilder calls, we can catch the initial parsing exceptions, but I haven't been able to figure out how to avoid a downstream NullReferenceException yet.

private void SetConfigRoot()
{
    var b = new ConfigurationBuilder().SetBasePath(AppDomain.CurrentDomain.BaseDirectory);
    b.AddYamlFile("app.config.yaml", true);
    b.AddJsonFile("app.config.json", true);
    b.SetFileLoadExceptionHandler((fleContext) =>
    {
        // This is hit whenever a config file is present but empty (or entirely comments).
        // Ideally, we would load defaults for an emtpy file and present a warning/error for bad JSON/YAML syntax.
        Resolver.Log.Error($"Error loading file configuration:: {fleContext.Exception}");
        this.ConfigurationRoot = null; // Still blows up later in "[External Code]"!
    });
    this.ConfigurationRoot = b.Build();
}

Error message:

System.NullReferenceException
Message=Object reference not set to an instance of an object.

[patridge]

Since app.config.* is a weird case, allowing JSON or YAML, I tried an empty YAML file with a populated JSON file.

Oddly, this doesn't appear to fail at all, and it grabs the config from the second JSON source just fine (due to order of adding file providers).

[patridge]

Even more strange. The reverse is not true. If you have a YAML file full of settings and an empty JSON file, it will still throw an exception and hit the SetFileLoadExceptionHandler action.

[patridge]

Should be addressed by #187.