Module returns pValue=NULL_PTR and ulValueLen=0 if CKA_LABEL asked in C_GetAttributeValue;
Searching for contacts whose email address matches exactly the email queried.
Using e_book_client_get_contacts_sync() could lead to trouble if the number of returned contacts happens to be enormous.

Switched to using Cursor to access contacts so contacts can be read iteratively.
Client cache was droped because it disturbs use of cursor.