public long getKeyHash() {
            return keyHash;
        }
The <tt>keyHash</tt> is stored because we may have duplicate entries for a
given hash bucket for two reasons:

<ol>
  <li> Multiple value insertions for the same key (standard multimap behaviour)
  <li> Hash collision. The key is different, but maps to the same bucket.
</ol>

We can use the stored hash to rapidly differentiate between these scenarios
and in various operations such as delete.

@param key the key
@param value the value
@param keyHash the hash <strong>(NB: full hash, not just bucket index!)</strong>
gateway/engine/beans/src/main/java/io/apiman/gateway/engine/beans/util/CaseInsensitiveStringMultiMap.java