While exploring the
found some typo error :
As per the documentation :
https://www.w3.org/TR/2013/REC-sparql11-http-rdf-update-20130321/#http-put
https://www.w3.org/TR/2013/REC-sparql11-http-rdf-update-20130321/#http-post
Although, API's behavior are correct for PUT [DROP Graph silently and INSERT DATA] and POST [INSERT DATA more of a merge.]
Regards,
Deepak Patwal