DROP named graph fails

I am using pystardog and have the following code ...
sparql = 'DROP GRAPH urn:e8dae583-f236-4ba5-a12f-39c956788916'
conn.begin()
conn.update(sparql)
conn.commit()

Studio shows that the indicated graph exists. (Select distinct ?g {graph ?g {?s ?p ?o}})

But I get the following error:
com.complexible.stardog.plan.eval.ExecutionException: Source graph urn:e8dae583-f236-4ba5-a12f-39c956788916 does not exist, cannot proceed with update.

Here are the details:

---------------------------------------------------------------------------
StardogException                          Traceback (most recent call last)
<ipython-input-18-8fc1042676bf> in <module>
      1 sparql = 'DROP GRAPH <urn:e8dae583-f236-4ba5-a12f-39c956788916>;'
      2 conn.begin()
----> 3 conn.update(sparql)
      4 conn.commit()

/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/stardog/connection.py in update(self, query, **kwargs)
    350           >>> conn.update('delete where {?s ?p ?o}')
    351         """
--> 352         self.conn.update(query, self.transaction, **kwargs)
    353 
    354     def is_consistent(self, graph_uri=None):

/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/stardog/http/connection.py in update(self, query, transaction, **kwargs)
     90 
     91     def update(self, query, transaction=None, **kwargs):
---> 92         self.__query(query, 'update', transaction, None, **kwargs)
     93 
     94     def __query(self,

/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/stardog/http/connection.py in __query(self, query, method, transaction, content_type, **kwargs)
    115                               method) if transaction else '/{}'.format(method)
    116 
--> 117         return self.client.post(
    118             url,
    119             data=params,

/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/stardog/http/client.py in post(self, path, **kwargs)
     27 
     28     def post(self, path, **kwargs):
---> 29         return self.__wrap(self.session.post(self.url + path, **kwargs))
     30 
     31     def put(self, path, **kwargs):

/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/stardog/http/client.py in __wrap(self, request)
     49                 msg = {'message': request.text}
     50 
---> 51             raise exceptions.StardogException('[{}] {}: {}'.format(
     52                 request.status_code, msg.get('code', ''), msg.get(
     53                     'message', '')))

StardogException: [500] QEQOE2: com.complexible.stardog.plan.eval.ExecutionException: Source graph urn:e8dae583-f236-4ba5-a12f-39c956788916 does not exist, cannot proceed with update.

Is there anything in stardog.log?

Checking for more detail. Also, rechecking the code that generated the graph.

Andrea