Creating new configuration blocks fail

[Zefeng-Wu]

When I used " iqtree_bestmodel" in species tree building, it gave an error after running for some minutes, and it reminded me that the "-safe" option should be added in iqtree command. So I create new configuration blocks by
ete3 build dump iqtree_bestmodel > myconfig.cfg
and I add an extra option of iqtree with "-safe=" in my configf files as followings:

[iqtree_bestmodel]
                                   -alrt = 1000
                                      -m = TESTNEWONLY
                                   -safe = 
                                   -seed = 31416
                                    _app = iqtree
                                   _desc = IQTree 

Then I rerun ete-build with -c myconfig.cfg, it can not run with an error :
ete3.tools.ete_build_lib.configobj.ConfigObjError: Parsing failed with several errors.
First error at line 532.

So how can I add the "-safe" option in my iqtree_bestmodel setup? Thanks