use isEmpty() instead of getLength() where appropriate
use isEmpty() instead of getLength() where appropriate

Change-Id: I2ac660a6035791e68af9bde9470bbf8c1d008dee

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core