value_from_ast: fixed coercing of null vars on non-nullable type

Replicates graphql/graphql-js@53afba1

Author: Cito

src/graphql/utilities/value_from_ast.py

@@ -52,15 +52,6 @@ def value_from_ast(
         # Importantly, this is different from returning the value null.
         return Undefined
 
-    if is_non_null_type(type_):
-        if isinstance(value_node, NullValueNode):
-            return Undefined
-        type_ = cast(GraphQLNonNull, type_)
-        return value_from_ast(value_node, type_.of_type, variables)
-
-    if isinstance(value_node, NullValueNode):
-        return None  # This is explicitly returning the value None.
-
     if isinstance(value_node, VariableNode):
         variable_name = value_node.name.value
         if not variables:
@@ -75,6 +66,15 @@ def value_from_ast(
         # is of the correct type.
         return variable_value
 
+    if is_non_null_type(type_):
+        if isinstance(value_node, NullValueNode):
+            return Undefined
+        type_ = cast(GraphQLNonNull, type_)
+        return value_from_ast(value_node, type_.of_type, variables)
+
+    if isinstance(value_node, NullValueNode):
+        return None  # This is explicitly returning the value None.
+
     if is_list_type(type_):
         type_ = cast(GraphQLList, type_)
         item_type = type_.of_type

tests/utilities/test_value_from_ast.py

@@ -66,6 +66,7 @@ def converts_enum_values_according_to_input_coercion_rules():
         assert _value_from('"BLUE"', test_enum) is Undefined
         assert _value_from("null", test_enum) is None
         assert _value_from("NULL", test_enum) is None
+        assert _value_from("NULL", GraphQLNonNull(test_enum)) is None
         assert isnan(_value_from("NAN", test_enum))
         assert _value_from("NO_CUSTOM_VALUE", test_enum) is Undefined
 
@@ -153,6 +154,7 @@ def accepts_variable_values_assuming_already_coerced():
         assert _value_from("$var", GraphQLBoolean, {}) is Undefined
         assert _value_from("$var", GraphQLBoolean, {"var": True}) is True
         assert _value_from("$var", GraphQLBoolean, {"var": None}) is None
+        assert _value_from("$var", non_null_bool, {"var": None}) is Undefined
 
     def asserts_variables_are_provided_as_items_in_lists():
         assert _value_from("[ $foo ]", list_of_bool, {}) == [None]