diff --git a/edge-agent-sdk/src/commonMain/kotlin/org/hyperledger/identus/walletsdk/domain/models/MessageAttachment.kt b/edge-agent-sdk/src/commonMain/kotlin/org/hyperledger/identus/walletsdk/domain/models/MessageAttachment.kt
index c29fca708..f655e0a4d 100644
--- a/edge-agent-sdk/src/commonMain/kotlin/org/hyperledger/identus/walletsdk/domain/models/MessageAttachment.kt
+++ b/edge-agent-sdk/src/commonMain/kotlin/org/hyperledger/identus/walletsdk/domain/models/MessageAttachment.kt
@@ -14,6 +14,7 @@ import kotlinx.serialization.json.JsonDecoder
 import kotlinx.serialization.json.JsonNames
 import kotlinx.serialization.json.jsonObject
 import org.hyperledger.identus.apollo.base64.base64UrlDecoded
+import org.hyperledger.identus.walletsdk.edgeagent.EdgeAgentError
 import java.util.UUID
 import kotlin.jvm.JvmOverloads
 
@@ -27,31 +28,19 @@ sealed class AttachmentData {
     /**
      * This method verifies the type of [AttachmentData] and returns the data as a json string.
      */
-    fun getDataAsJsonString(): String? {
+    fun getDataAsJsonString(): String {
         return when (this) {
-            is AttachmentHeader -> {
-                null
-            }
-
-            is AttachmentJws -> {
-                null
-            }
-
-            is AttachmentJwsData -> {
-                null
-            }
-
             is AttachmentBase64 -> {
                 this.base64.base64UrlDecoded
             }
 
-            is AttachmentLinkData -> {
-                null
-            }
-
             is AttachmentJsonData -> {
                 this.data
             }
+
+            else -> {
+                throw EdgeAgentError.AttachmentTypeNotSupported()
+            }
         }
     }
 
diff --git a/edge-agent-sdk/src/commonTest/kotlin/org/hyperledger/identus/walletsdk/edgeagent/EdgeAgentTests.kt b/edge-agent-sdk/src/commonTest/kotlin/org/hyperledger/identus/walletsdk/edgeagent/EdgeAgentTests.kt
index e73864832..bb48dcf4a 100644
--- a/edge-agent-sdk/src/commonTest/kotlin/org/hyperledger/identus/walletsdk/edgeagent/EdgeAgentTests.kt
+++ b/edge-agent-sdk/src/commonTest/kotlin/org/hyperledger/identus/walletsdk/edgeagent/EdgeAgentTests.kt
@@ -85,7 +85,6 @@ import org.junit.runner.RunWith
 import org.junit.runners.JUnit4
 import org.mockito.Mock
 import org.hyperledger.identus.walletsdk.pollux.models.PresentationSubmission
-import org.junit.Assert.assertNull
 import org.mockito.Mockito.verify
 import org.mockito.Mockito.`when`
 import org.mockito.MockitoAnnotations
@@ -1632,8 +1631,9 @@ class EdgeAgentTests {
             )
         )
         val attachments1 = message1.attachments
-        val attachmentDataString2 = attachments1.first().data.getDataAsJsonString()
-        assertNull(attachmentDataString2)
+        assertFailsWith<EdgeAgentError.AttachmentTypeNotSupported> {
+            attachments1.first().data.getDataAsJsonString()
+        }
     }
 
     val getCredentialDefinitionResponse =