[bfss] Make ``current_fs_path`` return None when an attribute has no value current_fs_path was returning the future fspath when no value was defined. * This does not make any sense * This tricks the storage into believing that updating the attribute content is not necessary. The file was written but the attributes was not updated. as a result the assignement was not made. (close #1725446)

\.svn
^build$
^dist$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data/database/.*\.sqlite
.*/data/database/.*\.config
.*/data/database/tmpdb.*