public Builder setHeader(String key, String value) {
            return setHeader(key, value == null ? null : new StringHeaderFactory(value));
        }
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>

<p> Use {@link #setHeader(String, LazyHeaderFactory)} if obtaining the value requires I/O
(ie an oauth token). </p>
core/src/main/java/com/bumptech/glide/load/model/LazyHeaders.java