private List<LazyHeaderFactory> getFactories(String key) {
            List<LazyHeaderFactory> factories = headers.get(key);
            if (factories == null) {
                factories = new ArrayList<LazyHeaderFactory>();
                headers.put(key, factories);
            }
            return factories;
        }
Replaces all existing {@link LazyHeaderFactory LazyHeaderFactorys} for the given key
with the given {@link LazyHeaderFactory}.

<p> If the given value is {@code null}, the header at the given key will be removed. </p>
core/src/main/java/com/bumptech/glide/load/model/LazyHeaders.java