How to fix null value date is returning date 12-31-1969

myObj = function MyObject(r) {
        this.Prop = r.Prop
        this.LogIn = new Date(r.LogIn)
        this.Created_Date = new Date(r.Created_Date)
    }

How do I assign empty value "" if r.LogIn is null otherwise Date.

Right now if LogIn is null, its assigning it to date 12-31-1969. 

myObj = function MyObject(r) {
        this.Prop = r.Prop
        this.LogIn = function(r){
		       if(r.LogIn ==null){
		           return "";
		       }
		     else{
		      return new Date(r.LogIn);
		     }
        this.Created_Date = new Date(r.Created_Date)
    }