hooks.ledger_entry: Warn when a template is unconfigured.

import2ledger/hooks/ledger_entry.py

@@ -3,6 +3,7 @@ import datetime
 import decimal
 import functools
 import io
+import logging
 import operator
 import re
 import tokenize
@@ -12,6 +13,8 @@ import babel.numbers
 from . import HOOK_KINDS
 from .. import errors, strparse
 
+logger = logging.getLogger('import2ledger.hooks.ledger_entry')
+
 class TokenTransformer:
     def __init__(self, source):
         try:
@@ -312,6 +315,8 @@ class LedgerEntryHook:
                 raise
         else:
             have_template = not template.is_empty()
-        if have_template:
+        if not have_template:
+            logger.warning("no Ledger template defined as %r", template_key)
+        else:
             with self.config.open_output_file() as out_file:
                 print(template.render(entry_data), file=out_file, end='')