Base Serializer class to store nullable values in DataStore

DataStoreNullableSerializer.kt

import androidx.datastore.core.DataStore
import androidx.datastore.core.Serializer
import java.io.InputStream
import java.io.OutputStream

abstract class NullableSerializer<T : Any> : Serializer<T?> {

    override val defaultValue: T? = null

    final override suspend fun readFrom(input: InputStream): T? {
        return if (input.isNotEmpty()) readNotNullFrom(input) else null
    }

    final override suspend fun writeTo(t: T?, output: OutputStream) {
        if (t != null) writeNotNullTo(t, output)
    }

    protected abstract fun readNotNullFrom(input: InputStream): T
    protected abstract fun writeNotNullTo(t: T, output: OutputStream)

    private fun InputStream.isNotEmpty() = available() > 0
}

suspend fun <T : Any> DataStore<T?>.clear() = updateData { null }

See also DataStoreSerializer