diff --git a/backend/src/main/kotlin/dev/dres/api/rest/types/evaluation/submission/ApiClientAnswer.kt b/backend/src/main/kotlin/dev/dres/api/rest/types/evaluation/submission/ApiClientAnswer.kt
index d746c840..2a9619f8 100644
--- a/backend/src/main/kotlin/dev/dres/api/rest/types/evaluation/submission/ApiClientAnswer.kt
+++ b/backend/src/main/kotlin/dev/dres/api/rest/types/evaluation/submission/ApiClientAnswer.kt
@@ -6,6 +6,7 @@ import dev.dres.data.model.media.MediaItemId
 import dev.dres.data.model.submissions.DbAnswer
 import dev.dres.data.model.submissions.DbAnswerType
 import io.javalin.openapi.OpenApiIgnore
+import io.javalin.openapi.OpenApiNullable
 import kotlinx.dnq.query.filter
 import kotlinx.dnq.query.singleOrNull
 import kotlinx.serialization.Serializable
@@ -21,6 +22,7 @@ import kotlinx.serialization.Serializable
 @Serializable
 data class ApiClientAnswer( //TODO add optional relevance score field
     /** The text that is part of this [ApiClientAnswer]. */
+    @get:OpenApiNullable
     val text: String? = null,
 
     /** The [MediaItemId] associated with the [ApiClientAnswer]. Is usually added as contextual information by the receiving endpoint. */
@@ -29,15 +31,19 @@ data class ApiClientAnswer( //TODO add optional relevance score field
     val mediaItemId: MediaItemId? = null,
 
     /** The name of the media item that is part of the answer. */
+    @get:OpenApiNullable
     val mediaItemName: String?  = null,
 
     /** The name of the collection the media item belongs to. */
+    @get:OpenApiNullable
     val mediaItemCollectionName: String? = null,
 
     /** For temporal [ApiClientAnswer]s: Start of the segment in question in milliseconds. */
+    @get:OpenApiNullable
     val start: Long? = null,
 
     /** For temporal [ApiClientAnswer]s: End of the segment in question in milliseconds. */
+    @get:OpenApiNullable
     val end: Long? = null,
 ) {
 
diff --git a/backend/src/main/kotlin/dev/dres/api/rest/types/evaluation/submission/ApiClientAnswerSet.kt b/backend/src/main/kotlin/dev/dres/api/rest/types/evaluation/submission/ApiClientAnswerSet.kt
index c3a9ad7d..c565a07c 100644
--- a/backend/src/main/kotlin/dev/dres/api/rest/types/evaluation/submission/ApiClientAnswerSet.kt
+++ b/backend/src/main/kotlin/dev/dres/api/rest/types/evaluation/submission/ApiClientAnswerSet.kt
@@ -6,6 +6,7 @@ import dev.dres.data.model.submissions.AnswerSetId
 import dev.dres.data.model.submissions.DbAnswerSet
 import dev.dres.data.model.submissions.DbVerdictStatus
 import io.javalin.openapi.OpenApiIgnore
+import io.javalin.openapi.OpenApiNullable
 import kotlinx.dnq.query.addAll
 import kotlinx.dnq.query.filter
 import kotlinx.dnq.query.first
@@ -21,7 +22,12 @@ import java.util.*
  * @version 1.0.0
  */
 @Serializable
-data class ApiClientAnswerSet(var taskId: String? = null, val taskName: String? = null, val answers: List<ApiClientAnswer>) {
+data class ApiClientAnswerSet(
+    @get:OpenApiNullable
+    var taskId: String? = null,
+    @get:OpenApiNullable
+    val taskName: String? = null,
+    val answers: List<ApiClientAnswer>) {
 
     /** The [AnswerSetId] of this [ApiClientAnswerSet]. Typically generated by the receiving endpoint. */
     @JsonIgnore
diff --git a/doc/oas-client.json b/doc/oas-client.json
index 7d7e9446..c86a9a59 100644
--- a/doc/oas-client.json
+++ b/doc/oas-client.json
@@ -2,8 +2,8 @@
   "openapi" : "3.0.3",
   "info" : {
     "title" : "DRES Client API",
-    "version" : "2.0.2",
-    "description" : "Client API for DRES (Distributed Retrieval Evaluation Server), Version 2.0.2"
+    "version" : "2.0.3-SNAPSHOT",
+    "description" : "Client API for DRES (Distributed Retrieval Evaluation Server), Version 2.0.3-SNAPSHOT"
   },
   "paths" : {
     "/api/v2/client/evaluation/currentTask/{evaluationId}" : {
@@ -1605,21 +1605,26 @@
         "additionalProperties" : false,
         "properties" : {
           "text" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "mediaItemName" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "mediaItemCollectionName" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "start" : {
             "type" : "integer",
-            "format" : "int64"
+            "format" : "int64",
+            "nullable" : true
           },
           "end" : {
             "type" : "integer",
-            "format" : "int64"
+            "format" : "int64",
+            "nullable" : true
           }
         }
       },
@@ -1628,10 +1633,12 @@
         "additionalProperties" : false,
         "properties" : {
           "taskId" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "taskName" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "answers" : {
             "type" : "array",
diff --git a/doc/oas.json b/doc/oas.json
index bb05416f..f64a75e6 100644
--- a/doc/oas.json
+++ b/doc/oas.json
@@ -2,8 +2,8 @@
   "openapi" : "3.0.3",
   "info" : {
     "title" : "DRES API",
-    "version" : "2.0.2",
-    "description" : "API for DRES (Distributed Retrieval Evaluation Server), Version 2.0.2",
+    "version" : "2.0.3-SNAPSHOT",
+    "description" : "API for DRES (Distributed Retrieval Evaluation Server), Version 2.0.3-SNAPSHOT",
     "contact" : {
       "name" : "The DRES Dev Team",
       "url" : "https://dres.dev"
@@ -6019,21 +6019,26 @@
         "additionalProperties" : false,
         "properties" : {
           "text" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "mediaItemName" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "mediaItemCollectionName" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "start" : {
             "type" : "integer",
-            "format" : "int64"
+            "format" : "int64",
+            "nullable" : true
           },
           "end" : {
             "type" : "integer",
-            "format" : "int64"
+            "format" : "int64",
+            "nullable" : true
           }
         }
       },
@@ -6042,10 +6047,12 @@
         "additionalProperties" : false,
         "properties" : {
           "taskId" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "taskName" : {
-            "type" : "string"
+            "type" : "string",
+            "nullable" : true
           },
           "answers" : {
             "type" : "array",