diff --git a/src/vtlengine/AST/ASTTemplate.py b/src/vtlengine/AST/ASTTemplate.py
index 78ff8ecc..871712db 100644
--- a/src/vtlengine/AST/ASTTemplate.py
+++ b/src/vtlengine/AST/ASTTemplate.py
@@ -268,7 +268,8 @@ def visit_Aggregation(self, node: AST.Aggregation) -> None:
                 for group in node.grouping:
                     self.visit(group)
         """
-        self.visit(node.operand)
+        if node.operand is not None:
+            self.visit(node.operand)
 
         if node.grouping is not None:
             for group in node.grouping: