After searching through repository of Mayocat, I found this:
And then followed the link, and found this:
And then I found out that this bug was cause by JDK7, package
probeContentType(Path path) and this feature was broken on Mac OS X (More details here).
However, this bug should be fixed in JDK8, mine was still not working although my working environment was under JDK8. Then I checked the Oracle Bug Database and it seems that it need a file
.mime.types(you can download one sample file here or simply get it from your apache server or nginx server) in $HOME/ directory.
After adding the file
~/ (remember to clear the browser cache!), everything was ok then :).