diff --git a/xls2ddl/tmpls.py b/xls2ddl/tmpls.py
index 10c3450..2f51ef1 100644
--- a/xls2ddl/tmpls.py
+++ b/xls2ddl/tmpls.py
@@ -374,12 +374,12 @@ _validation_rules = json.loads(r'''{{validation_rules}}''')
 import re as _re
 _errors = []
 for _fname, _rules in _validation_rules.items():
-\t_val = params_kw.get(_fname, '')
-\tif _val is None: _val = ''
-\t_val = str(_val)
-\t# Update: skip validation if field is empty (not modified)
-\tif not _val or _val.strip() == '':
+\tif _fname not in params_kw:
 \t\tcontinue
+\t_val = params_kw.get(_fname)
+\tif _val is None or str(_val).strip() == '':
+\t\tcontinue
+\t_val = str(_val)
 \tfor _rule in _rules:
 \t\t_rt = _rule.get('type', '')
 \t\t_rm = _rule.get('message', _fname)