@Override
    public Set<String> keySet() {
        return readMethods.keySet();
    }
Get the keys for this BeanMap.
<p>
Write-only properties are <b>not</b> included in the returned set of
property names, although it is possible to set their value and to get
their type.

@return BeanMap keys.  The Set returned by this method is not
        modifiable.
querydsl-core/src/main/java/com/querydsl/core/util/BeanMap.java