I have a problem when serializing the response to model using com.openai.models.chat.completions.StructuredChatCompletionCreateParams

My model

data class Metadata(
    @JsonProperty("expected_result")
    @field:Schema(name = "expected_result")
    @JsonPropertyDescription("Expected result of a step.")
    val expectedResult: String?,

    @JsonPropertyDescription("What data users should provide.")
    val data: String?
)

When I call client.chat()..... with this model as Structured Response, the expectedResult always null

But when I change my model to

    val expected_result: String?,

I got the response correctly.

What happens with it, do we have problem with the serializer?