upsert_all() throws issue when upserting to empty table

If I try to add a list of dicts to an empty table using upsert_all, I get an error:

import sqlite3
from sqlite_utils import Database
import pandas as pd

conx = sqlite3.connect(':memory')
cx = conx.cursor()
cx.executescript('CREATE TABLE "test" ("Col1" TEXT);')

q="SELECT * FROM test;"
pd.read_sql(q, conx) #shows empty table

db = Database(conx)
db['test'].upsert_all([{'Col1':'a'},{'Col1':'b'}])

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-74-8c26d93d7587> in <module>
      1 db = Database(conx)
----> 2 db['test'].upsert_all([{'Col1':'a'},{'Col1':'b'}])

/usr/local/lib/python3.7/site-packages/sqlite_utils/db.py in upsert_all(self, records, pk, foreign_keys, column_order, not_null, defaults, batch_size, hash_id, alter, extracts)
   1157             alter=alter,
   1158             extracts=extracts,
-> 1159             upsert=True,
   1160         )
   1161 

/usr/local/lib/python3.7/site-packages/sqlite_utils/db.py in insert_all(self, records, pk, foreign_keys, column_order, not_null, defaults, batch_size, hash_id, alter, ignore, replace, extracts, upsert)
   1040                     sql = "INSERT OR IGNORE INTO [{table}]({pks}) VALUES({pk_placeholders});".format(
   1041                         table=self.name,
-> 1042                         pks=", ".join(["[{}]".format(p) for p in pks]),
   1043                         pk_placeholders=", ".join(["?" for p in pks]),
   1044                     )

TypeError: 'NoneType' object is not iterable

A hacky workaround in use is:

try:
  db['test'].upsert_all([{'Col1':'a'},{'Col1':'b'}])
except:
  db['test'].insert_all([{'Col1':'a'},{'Col1':'b'}])

[simonw]

I think this is because you forgot to include a pk= argument. I’ll change the code to throw a more useful error in this case.

[psychemedia]

So the conundrum continues… The simple test case above now runs, but if I upsert a large number of new records (successfully) and then try to upsert a fewer number of new records to a different table, I get the same error.

If I run the same upserts again (which in the first case means there are no new records to add, because they were already added), the second upsert works correctly.

It feels as if the number of items added via an upsert >> the number of items I try to add in an upsert immediately after, I get the error.