@Override
    public IStringMultiMap clear() {
        hashArray = new Element[hashArray.length];
        keyCount = 0;
        return this;
    }
A simple multimap able to accept multiple values for a given key.
<p>
The implementation is specifically tuned for headers (such as HTTP), where
the number of entries tends to be moderate, but are frequently accessed.
</p>
<p>
This map expects ASCII for key strings.
</p>
<p>
Case is ignored (avoiding {@link String#toLowerCase()} <code>String</code> allocation)
before being hashed (<code>xxHash</code>).
</p>
<p>
    Constraints:
<ul>
  <li><strong>Not thread-safe.</strong></li>
  <li><tt>Null</tt> is <strong>not</strong> a valid key.</li>
</ul>
</p>

@author Marc Savy {@literal <msavy@redhat.com>}
gateway/engine/beans/src/main/java/io/apiman/gateway/engine/beans/util/CaseInsensitiveStringMultiMap.java