chore: apply suggestions from code review

Co-authored-by: Phillip Cloud <[email protected]>

Author: NickCrews

ibis/expr/types/relations.py

@@ -4625,7 +4625,8 @@ def value_counts(self, *, name: str | None = None) -> ir.Table:
         └───────┴───────────┴───────────────────┘
         """
         columns = self.columns
-        name = name or "_".join(columns) + "_count"
+        if name is None:
+        	name = "_".join(columns) + "_count"
         return self.group_by(columns).agg(lambda t: t.count().name(name))
 
     def unnest(