Java out of bounds exception whilst inserting into alphabetical and numerical sorted array

Question

I am creating an array that stores rental properties in a sorted order. Firstly alphabetical and if towns match then it should be lowest value rent placed first. The method runs fine when I only check for the alphabetical order but when I try to add in to check the rent I always get the out of bounds exception (ArrayIndexOutOfBoundsException: -1) at line 62 which is

if(this.propertyList[location].getTown().compareToIgnoreCase(town)==0){

and I dunno why.

public void insert(String reference, String town, Integer rent, Integer bedrooms) {
    Integer location = propertyListSize-1;//start at end of array
        while (location >=0 && this.propertyList[location].getTown().compareToIgnoreCase(town) > 0) {
            this.propertyList[location + 1] = this.propertyList[location];//bump item up to next location
            location = location - 1;//move to next location
            if(this.propertyList[location].getTown().compareToIgnoreCase(town)==0){
                if(this.propertyList[location].getRent().compareTo(rent)>0)/*rent bigger than new*/{
                    this.propertyList[location + 1] = this.propertyList[location];//bump item up to next location
                }
            }
        }
            this.propertyList[location + 1] = new Residential(reference, town, rent, bedrooms);
            this.propertyListSize++;
        }