[BUG] [kotlin-spring] MissingKotlinParameterException instead of BeanValidation exception for missing required property

Created by: cthiebault

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
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Description

I defined a required property but instead of getting a bean validation exception, I get a MissingKotlinParameterException:

com.fasterxml.jackson.module.kotlin.MissingKotlinParameterException: Instantiation of [simple type, class dto.Component] value failed for JSON property type due to missing (therefore NULL) value for creator parameter type which is a non-nullable type
 at [Source: (PushbackInputStream); line: 1, column: 2] (through reference chain: dto.Component["type"])

Here is the generated DTO:

data class Component (
        @get:NotNull 
        @ApiModelProperty(required = true, value = "")
        @JsonProperty("type") val type: kotlin.String,

        @ApiModelProperty(value = "")
        @JsonProperty("model") val model: kotlin.String? = null
) 

It seems validation is done after the dto is instantiated... and as a required field is null, it can't create a new instance of this dto.

openapi-generator version

kotlin-spring with 4.2.2

OpenAPI declaration file content or url

Component:
  type: object
  required:
    - type
  properties:
    type:
      type: string
    model:
      type: string