private static String[] checkSourcesSyntax(String sources) {
        String[] sourceSet = null;
        if (sources != null) {
            sourceSet = sources.split(",");
            int i = 0;
            for (String s : sourceSet) {
                if (!s.startsWith("tcp/")) {
                    sourceSet[i] = "tcp/" + sourceSet[i];
                }
                i++;
            }
        }
        return sourceSet;
    }
Check sources syntax and convert it to a proper source set by checking if
sources start with the required "tcp/" prefix and add that prefix if not.

@param sources a source set as a comma-separated string
@return a String array with sources, or null if the input source set was null
config/src/main/java/com/yahoo/config/subscription/ConfigSourceSet.java