Fix division by zero.

Also add a regression test.

src/ledgerhelpers/journal.py

@@ -309,7 +309,7 @@ def harvest_accounts_and_last_commodities(self):
             for subpost in post.xact.posts():
                 if str(subpost.account) not in accts:
                     accts.append(str(subpost.account))
-                comm = subpost.amount / subpost.amount
+                comm = ledger.Amount(1).with_commodity(subpost.amount.commodity)
                 comm.commodity = comm.commodity.strip_annotations()
                 commos[str(subpost.account)] = str(comm)
                 amts[str(comm)] = True

tests/test_ledgerhelpers.py

@@ -45,6 +45,12 @@ def test_transactions_with_payee_match(self):
         ts = journal.transactions_with_payee("beer", j.internal_parsing())
         self.assertEqual(ts[0].payee, "beer")
 
+    def test_transaction_with_zero_posting(self):
+        c = base.datapath("zero.dat")
+        j = journal.Journal.from_file(c, None)
+        _, commos = j.accounts_and_last_commodity_for_account()
+        self.assertEqual(commos["rest"], "1 USD")
+
 
 class TestGenerateRecord(T):
 

tests/testdata/zero.dat

@@ -0,0 +1,4 @@
+2022-01-01 zero
+ ac1  1 USD
+ ac2  -1 USD
+ rest