Fixes variable values of non-null type with default value

Replicates graphql/graphql-js@Fixes variable values of non-null type with default value

Author: Cito

README.md

@@ -16,7 +16,7 @@ The current version 3.0.0b1 of GraphQL-core is up-to-date
 with GraphQL.js version 14.5.6.
 
 All parts of the API are covered by an extensive test suite
-of currently 1989 unit tests.
+of currently 1990 unit tests.
 
 
 ## Documentation

src/graphql/execution/values.py

@@ -94,8 +94,7 @@ def coerce_variable_values(
                 coerced_values[var_name] = value_from_ast(
                     var_def_node.default_value, var_type
                 )
-
-            if is_non_null_type(var_type):
+            elif is_non_null_type(var_type):
                 var_type_str = inspect(var_type)
                 on_error(
                     GraphQLError(

tests/execution/test_variables.py

@@ -546,6 +546,17 @@ def allows_nullable_inputs_to_be_set_to_a_value_directly():
             assert result == ({"fieldWithNullableStringInput": "'a'"}, None)
 
     def describe_handles_non_nullable_scalars():
+        def allows_non_nullable_variable_to_be_omitted_given_a_default():
+            result = execute_query(
+                """
+                query ($value: String! = "default") {
+                  fieldWithNullableStringInput(input: $value)
+                }
+                """
+            )
+
+            assert result == ({"fieldWithNullableStringInput": "'default'"}, None)
+
         def allows_non_nullable_inputs_to_be_omitted_given_a_default():
             result = execute_query(
                 """