public void map(Class<? extends Exception> exceptionClass, ExceptionHandlerImpl handler) {
        this.exceptionMap.put(exceptionClass, handler);
    }
Maps the given handler to the provided exception type. If a handler was already registered to the same type, the
handler is overwritten.

@param exceptionClass Type of exception
@param handler        Handler to map to exception
src/main/java/spark/ExceptionMapper.java