Check which combinations of parameters are null in Java

I am new to Java. I am facing an issue now in which I couldn't find the easiest and cleanest way of solving it.

Suppose I have 3 parameters(string) passed to a function(could be a Hashmap too).I want to check if individual variable or combination of variables is not Null and act accordingly.

For example one way to do this is using if-else this way

if(a!=null && b == null && c == null) { 
      //doSomething   
}
 else if(a==null && b!= null && c == null ) { 
     //doSomething 
}
 else if(a==null && b0= null && c != null) { 
     //doSomething 
}
  ......
    //Similarly combination of two variables
 if(a!=null && b != null && c == null) {
     //doSomething 
}
 else if(a!=null && b== null && c != null) { 
    //doSomething
}
 else if(a==null && b!= null && c != null) { 
    //doSomething 
} 
  ......
    //and so on 
    //Similarly combination of three variables
 if(a!=null && b != null && c != null) {
    //doSomething 
}

   ....

How to achieve this kind of situation. I found similar question, but didn't make the code clean. Any help will be appreciated