in absence of sth/sb 里面的sth/sb常常是泛指的
in the absence of sth/sb 里面的sth/sb常常是特定的例如：In absence of laws,MFIs create own code of conduct.
In the absence of the law of Entropy,this state is free from all stress - the state of Absolute Bliss.
泛指和特指不明确的时候也可以混用.
个人看法,供参考.