public bool IsPackageSourceEnabled(PackageSource source)
        {
            if (source == null)
            {
                throw new ArgumentNullException("source");
            }

            var value = Settings.GetValue(ConfigurationConstants.DisabledPackageSources, source.Name);

            // It doesn't matter what value it is.
            // As long as the package source name is persisted in the <disabledPackageSources> section, the source is disabled.
            return(string.IsNullOrEmpty(value));
        }