[BUG] Inaccurate generation for Rust

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.

Reproduce the issue with the supplied testcase.yaml and Docker generation command, then compare the generated Rust model with the expected output. Start by tracing the Rust generator data passed to the custom template, especially the reported isNullable flag for each field. Done means required and optional nullable/non-nullable properties produce the expected Rust types and serde attributes.