Is there a way to use the default value on a non-optional parameter when null is passed?

You can define a companion object for your data class and overload its invoke operator to use default values when null is passed:

data class Data private constructor(
    val name: String,
    val number: Long
) {
    companion object {
        operator fun invoke(
            name: String? = null,
            number: Long? = null
        ) = Data(
            name ?: "",
            number ?: 0
        )
    }
}