Unable to borrow value returned from definitions_mut() function

example code: [Note - I have added the references correctly. Also, I am new to Rust, sorry in advance for my naiveite]
```rs
impl OpenApiResponderInner for XYZ{
fn responses(
gen: &mut OpenApiGenerator,
) -> std::result::Result {
let mut content = Map::new();
let settings = schemars::gen::SchemaSettings::default().with(|s| {
s.option_nullable = true;
s.option_add_null_type = false;
s.definitions_path = "#/components/schemas/".to_string();
});

let mut schema_generator = settings.into_generator();
let schema = schema_generator.root_schema_for::();

let definitions = gen.schema_generator().definitions_mut(); //error[E0596]: cannot borrow data in a `&` reference as mutable
for (key, value) in schema.definitions {
definitions.insert(key, value);
}
}
```