Bug 13957: If no value, display an empty string instead of "null"

Bug 13957: If no value, display an empty string instead of "null"

Using the autocomplete feature in the patron search, if one value is
missing (i.e. country), it will be replaced with 'null'.
The default value should be an empty string.

Test plan:
0/ Enable the patron autocomplete feature
1/ Create a patron without value for country, address, zipcode, city
2/ Go on the circ home page
3/ Search for this patron. The country should not have been replaced by
"null".

Signed-off-by: Nicolas Legrand <nicolas.legrand@bulac.fr>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>