@Override
    public void visitMembers(ObjectVisitor visitor) {
        super.visitMembers(visitor);
        visitor.visit("keyAttribute", keyAttribute);
        visitor.visit("valueAttribute", valueAttribute);
        visitor.visit("key", key);
        visitor.visit("keySourceAttribute", keySourceAttribute);
    }
This function is an instruction to do a lookup in a map attribute, returning the value.

The key is either specified explicitly or found via a key source attribute.
Two underlying attributes are used to represent the map attribute (the key and value attributes).

@author geirst
searchlib/src/main/java/com/yahoo/searchlib/expression/AttributeMapLookupNode.java