[BUG][Kotlin] Wrong default value is generated if the field type is BigDecimal

Created by: alitams

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

If one of the type's mapping value is BigDecimal, and sets a default value, then a simple Int is given to the value.

Generated:

val bar: java.math.BigDecimal? = 0

Expected:

val bar: java.math.BigDecimal? = java.math.BigDecimal.ZERO

(or BigDecimal(0))

openapi-generator version

5.3.0

OpenAPI declaration file content or url

...
schemas:
  Foo:
      description: 'Xy'
      type: object
      properties:
        bar:
          type: number
          default: 0

Generation Details

java -jar -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005 modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
   -i xy.yaml \
   -g kotlin-client \
   -o gen/generated \
   --additional-properties=library=jvm-retrofit2,useRxJava3=true,dateLibrary=threetenbp-localdatetime,enumPropertyNaming=UPPERCASE,serializationLibrary=jackson,enablePostProcessFile=true 

Steps to reproduce

Generate the code below, and check the result.

Related issues/PRs

Suggest a fix

The BigDecimal should handled to generate the schema well.

For example:

    override fun toDefaultValue(schema: Schema<*>?): String? {
        val referencedSchema = ModelUtils.getReferencedSchema(this.openAPI, schema)
        val defaultValue =
            if (referencedSchema.default is BigDecimal) {
                getBigDecimalDefaultValue(referencedSchema.default as BigDecimal)
            } else {
                super.toDefaultValue(schema)
            }

        return defaultValue ?: referencedSchema.default?.toString()
    }