Configuration#getTimeDuration is not consistent between default value and manual settings.

When call getTimeDuration like this:

conf.getTimeDuration("nn.interval", 10, TimeUnit.SECONDS, TimeUnit.MILLISECONDS);

 If "nn.interval" is set manually or configured in xml file, 10000 will be retrurned.
If not, 10 will be returned while 10000 is expected.
The logic is not consistent.