diff --git a/cms-plugin-framework/src/main/java/org/gcube/application/cms/plugins/requests/BaseRequest.java b/cms-plugin-framework/src/main/java/org/gcube/application/cms/plugins/requests/BaseRequest.java
index bad3de3..12cb4a4 100644
--- a/cms-plugin-framework/src/main/java/org/gcube/application/cms/plugins/requests/BaseRequest.java
+++ b/cms-plugin-framework/src/main/java/org/gcube/application/cms/plugins/requests/BaseRequest.java
@@ -41,11 +41,7 @@ public class BaseRequest {
 
     public static final String getMandatory(String param,Document params) throws InvalidPluginRequestException {
         if(params==null || params.isEmpty()|| !params.containsKey(param)) throw new InvalidPluginRequestException("Missing mandatory parameter "+param);
-        try {
-            return Serialization.write(params.get(param));
-        } catch (JsonProcessingException e) {
-            throw new InvalidPluginRequestException(e);
-        }
+        return Serialization.convert(params.get(param),String.class);
     }
 
     public BaseRequest validate() throws InvalidPluginRequestException {