[BUG] Inaccurate generation for Rust

[magniff]

Version: 7.0.0-SNAPSHOT
Command: docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli generate -g rust -i /local/openapi/testcase.yaml -o /local/out/rust

Spec:

openapi: 3.1.0
info:
  version: '1.0'
  title: "testy test"
paths: {}
components:
  schemas:
    TestObject:
      type: object
      title: UpdateRequest
      required:
        - required_nonnull
        - required_nullable
      properties:
        optional_nonnull:
          type: string
          nullable: false
        required_nonnull:
          type: string
          nullable: false
        optional_nullable:
          type: string
          nullable: true
        required_nullable:
          type: string
          nullable: true

Reality:

#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
pub struct TestObject {
    #[serde(rename = "optional_nonnull", default, with = "::serde_with::rust::double_option", skip_serializing_if = "Option::is_none")]
    pub optional_nonnull: Option<Option<serde_json::Value>>,
    #[serde(rename = "required_nonnull", deserialize_with = "Option::deserialize")]
    pub required_nonnull: Option<serde_json::Value>,
    #[serde(rename = "optional_nullable", default, with = "::serde_with::rust::double_option", skip_serializing_if = "Option::is_none")]
    pub optional_nullable: Option<Option<serde_json::Value>>,
    #[serde(rename = "required_nullable", deserialize_with = "Option::deserialize")]
    pub required_nullable: Option<serde_json::Value>,
}

Expected:

#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
pub struct TestObject {
    #[serde(rename = "optional_nonnull", skip_serializing_if = "Option::is_none")]
    pub optional_nonnull: Option<String>,
    #[serde(rename = "required_nonnull")]
    pub required_nonnull: String,
    #[serde(rename = "optional_nullable", default, with = "::serde_with::rust::double_option", skip_serializing_if = "Option::is_none")]
    pub optional_nullable: Option<Option<String>>,
    #[serde(rename = "required_nullable")]
    pub required_nullable: Option<String>,
}

Thoughts

I dont see how I can turn reality into expected using configuration keys from here. Overall, why is reality so off?

Update

After messing around with a custom template I found out that for each field the flag isNullable=true is passed to the template, which seem to be a bug somewhere in generator.