searching technic on multiple paramters which may be null : I am trying to implement searching technic which will take four parameters and returns a set of matched results.  
method signature looks like  

    public Set<Mobile> search(Set<Mobile> mobiles, OperatingSystem os,
			Brand brand,Display display, Style style);

parameters may be null if they don't want to search for that particular property.ex: operatingSystem may be null but a user may provide brand, display and style.

I have tried with all 16 possible combinations like by checking null on each property which I feel not a good option. 

Thanks in advance.
