Bugfix: Calling count with None arguments (#768)

* Small bugfix. When arguments are None, we should use count_star

* When no arguments are given to count, set argument to lit(1) so that it is similar to count_star but still enables you to select distinct=True.

python/datafusion/functions.py

@@ -1295,6 +1295,8 @@ def corr(value1: Expr, value2: Expr, distinct: bool = False) -> Expr:
 
 def count(args: Expr | list[Expr] | None = None, distinct: bool = False) -> Expr:
     """Returns the number of rows that match the given arguments."""
+    if args is None:
+        return count(Expr.literal(1), distinct=distinct)
     if isinstance(args, list):
         args = [arg.expr for arg in args]
     elif isinstance(args, Expr):