Here is a template (test1.xls) allowing a simple reproduction of the problem. Please note that I'm using the multisheet feature of JXLS.
When the if-condition is true (the site has an address) the result is displayed as expected But when it's false and no adress is displayed I lose 2 rows, number 7 and 8, replaced by blanks rows. (result in res.xls)
Find my test sources in attachment.