fix default value for abstract to be empty string
fix default value for abstract to be empty string

nikken1/patentprocessor,yngcan/patentprocessor,nikken1/patentprocessor,funginstitute/patentprocessor,funginstitute/patentprocessor,yngcan/patentprocessor,nikken1/patentprocessor,yngcan/patentprocessor,funginstitute/patentprocessor