diff --git a/BankingClientModel/src/commonMain/kotlin/net/codinux/banking/client/model/tan/FlickerCode.kt b/BankingClientModel/src/commonMain/kotlin/net/codinux/banking/client/model/tan/FlickerCode.kt
index 8fb77557..a39f0620 100644
--- a/BankingClientModel/src/commonMain/kotlin/net/codinux/banking/client/model/tan/FlickerCode.kt
+++ b/BankingClientModel/src/commonMain/kotlin/net/codinux/banking/client/model/tan/FlickerCode.kt
@@ -7,13 +7,13 @@ import net.codinux.banking.client.model.config.NoArgConstructor
 @NoArgConstructor
 open class FlickerCode(
     val challengeHHD_UC: String,
-    val parsedDataSet: String,
+    val parsedDataSet: String? = null,
     val decodingError: String? = null
 ) {
 
     @get:JsonIgnore
     val decodingSuccessful: Boolean
-        get() = decodingError == null
+        get() = parsedDataSet != null
 
 
     override fun toString(): String {
diff --git a/BankingClientModel/src/commonMain/kotlin/net/codinux/banking/client/model/tan/TanImage.kt b/BankingClientModel/src/commonMain/kotlin/net/codinux/banking/client/model/tan/TanImage.kt
index da739a76..b58f9c4a 100644
--- a/BankingClientModel/src/commonMain/kotlin/net/codinux/banking/client/model/tan/TanImage.kt
+++ b/BankingClientModel/src/commonMain/kotlin/net/codinux/banking/client/model/tan/TanImage.kt
@@ -6,22 +6,22 @@ import net.codinux.banking.client.model.config.NoArgConstructor
 @Suppress("RUNTIME_ANNOTATION_NOT_SUPPORTED")
 @NoArgConstructor
 open class TanImage(
-    val mimeType: String,
-    val imageBytesBase64: String,
+    val mimeType: String? = null,
+    val imageBytesBase64: String? = null,
     val decodingError: String? = null
 ) {
 
     @get:JsonIgnore
     val decodingSuccessful: Boolean
-        get() = decodingError == null
+        get() = mimeType != null && imageBytesBase64 != null
 
 
     override fun toString(): String {
-        if (decodingSuccessful == false) {
-            return "Decoding error: $decodingError"
+        mimeType?.let {
+            return mimeType
         }
 
-        return mimeType
+        return "Decoding error: $decodingError"
     }
 
 }
\ No newline at end of file
diff --git a/FinTs4jBankingClient/src/commonMain/kotlin/net/codinux/banking/client/fints4k/FinTs4kMapper.kt b/FinTs4jBankingClient/src/commonMain/kotlin/net/codinux/banking/client/fints4k/FinTs4kMapper.kt
index 75f3832c..51d1eec7 100644
--- a/FinTs4jBankingClient/src/commonMain/kotlin/net/codinux/banking/client/fints4k/FinTs4kMapper.kt
+++ b/FinTs4jBankingClient/src/commonMain/kotlin/net/codinux/banking/client/fints4k/FinTs4kMapper.kt
@@ -338,7 +338,11 @@ open class FinTs4kMapper {
         TanImage(image.mimeType, mapToBase64(image.imageBytes), mapException(image.decodingError))
 
     @OptIn(ExperimentalEncodingApi::class)
-    protected open fun mapToBase64(bytes: ByteArray): String {
+    protected open fun mapToBase64(bytes: ByteArray?): String? {
+        if (bytes == null || bytes.isEmpty()) {
+            return null
+        }
+
         return Base64.Default.encode(bytes)
     }