public static boolean isGenerationNewer(long newGen, long oldGen) {
        return (oldGen < newGen) || (newGen == 0);
    }
Loop through values and return the first one that is set and non-empty.

@param defaultValue The default value to use if no environment variables are set.
@param envVars      one or more environment variable strings
@return a String with the value of the environment variable
config/src/main/java/com/yahoo/vespa/config/util/ConfigUtils.java