Having trouble with arrays in java

So, this is a simple question.

I created this for-loop so that the user can input different types of vehicles, depending on how many they want to rent (from previous code). However, when I check the values within the array list, it says this:

nullMotorbike

null

When I want it to say this (I am inputting Motorbike and car):

Motorbike

Car

Here is the for-loop:

    vehicleTypes = new String[numOfVehicles+1];
    
    for(int i = 0; i < vehicleTypes.length; i++) {
        System.out.println("What vehicle type would you like? Motorbike, trailer, or car?: ");
        vehicleType = ReadStringFromUser();
        if(vehicleType.equals("Motorbike") || vehicleType.equals("Trailer") || vehicleType.equals("Car")) {
            vehicleTypes[i] += vehicleType;
        }

System.out.println(vehicleTypes[i]);