LPS-52310 - Web Form portlet show NULL value in the Options text field

this issue is caused by "NULL" value, the fix reason as follow:

:1234:in the branch of ee-6.2.x ,using "String xml = String.Blank", but in branch of trunk,using "String xml =NULL"

:1234: if using "String xml = NULL",we need to judge the value everywhere if they are necessary

:1234: search the same using "String xml = null ", it won,t impact other functions,please double check.