don't error when completing parameter-less functions

pgcli/packages/function_metadata.py

@@ -138,12 +138,12 @@ def parse_typed_field_list(tokens):
 
 def field_names(sql, mode_filter=('IN', 'OUT', 'INOUT', 'VARIADIC')):
     """Yields field names from a table declaration"""
+
+    if not sql:
+        return
+
     # sql is something like "x int, y text, ..."
     tokens = sqlparse.parse(sql)[0].flatten()
     for f in parse_typed_field_list(tokens):
         if f.name and (not mode_filter or f.mode in mode_filter):
             yield f.name
-
-
-
-

tests/test_function_metadata.py

@@ -54,3 +54,7 @@ def test_argument_names():
     assert list(names) == ['y']
 
 
+def test_empty_arg_list():
+    # happens for e.g. parameter-less functions like now()
+    names = field_names('')
+    assert list(names) == []