also support string_value not equal empty string
also support string_value not equal empty string

ahmadassaf/open-data-certificate,Motejl/open-data-certificate,zoul/open-data-certificate,zoul/open-data-certificate,ahmadassaf/open-data-certificate,istvan-antal/open-data-certificate,theodi/open-data-certificate,Motejl/open-data-certificate,zoul/open-data-certificate,istvan-antal/open-data-certificate,Motejl/open-data-certificate,istvan-antal/open-data-certificate,theodi/open-data-certificate,ahmadassaf/open-data-certificate,theodi/open-data-certificate,theodi/open-data-certificate,ahmadassaf/open-data-certificate,zoul/open-data-certificate,Motejl/open-data-certificate