insert_all() / .upsert_all() work with empty list (#64)

Closes #52

sqlite_utils/db.py

@@ -977,7 +977,10 @@ class Table(Queryable):
         # we need to adjust the batch_size down if we have too many cols
         records = iter(records)
         # Peek at first record to count its columns:
-        first_record = next(records)
+        try:
+            first_record = next(records)
+        except StopIteration:
+            return self  # It was an empty list
         num_columns = len(first_record.keys())
         assert (
             num_columns <= SQLITE_MAX_VARS

tests/test_create.py

@@ -789,3 +789,12 @@ def test_drop_view(fresh_db):
     assert ["foo_view"] == fresh_db.view_names()
     assert None is fresh_db["foo_view"].drop()
     assert [] == fresh_db.view_names()
+
+
+def test_insert_upsert_all_empty_list(fresh_db):
+    fresh_db["t"].insert({"foo": 1})
+    assert 1 == fresh_db["t"].count
+    fresh_db["t"].insert_all([])
+    assert 1 == fresh_db["t"].count
+    fresh_db["t"].upsert_all([])
+    assert 1 == fresh_db["t"].count