private void validateServicesFile() throws IOException {
        File servicesFile = getServicesFile();
        if ( ! servicesFile.exists())
            throw new IllegalArgumentException(SERVICES + " does not exist in application package. " +
                                               "There are " + filesInApplicationPackage() + " files in the directory");
        if (IOUtils.readFile(servicesFile).isEmpty())
            throw new IllegalArgumentException(SERVICES + " in application package is empty. " +
                                               "There are " + filesInApplicationPackage() + " files in the directory");
    }
Reads a ranking expression from file to a string and returns it.

@param name the name of the file to return,
            relative to the search definition directory in the application package
@return the content of a ranking expression file
@throws IllegalArgumentException if the file was not found or could not be read
config-application-package/src/main/java/com/yahoo/config/model/application/provider/FilesApplicationPackage.java