typeof(Functions).Assembly.Location returns empty string, yet shows proper value in debugger

public string GetLicenseFileName()
{
var path = Path.ChangeExtension(typeof(Functions).Assembly.Location, "lic");
return path;
}

///
/// Get key from file having name of calling assembly with extension .lic
///
///
public string GetKeyFromFile()
{
string key = null;

string path = GetLicenseFileName();

if (!File.Exists(path))
{
throw new Exception($"Unable to locate a valid license file. {path}");
}

key = File.ReadAllText(path);

return key;
}

In the code above GetLicenseFileName always returns empty string!!! Inside the Excel DNA functions!!!