About the "null" error

I am working on a workflow. I created an expression. I want it to appear on the screen when the user enters multiple data. However, whenever multiple entries are made, it brings "null" to the beginning of the attribute value. The html code I created to appear on the screen and the screenshot of the Error are attached.

I request your help.

com.ptc.core.lwc.server.PersistableAdapter obj = new com.ptc.core.lwc.server.PersistableAdapter(primaryBusinessObject,null,null,null);

obj.load("REF_TEKLIF_NO");

Object value= obj .get("REF_TEKLIF_NO");

if (value instanceof Object[]) {

Object values[] = (Object[]) value;

for(int vv=0; vv < values.length; vv++)

{ REF_TEKLIF_NO = REF_TEKLIF_NO + (vv == 0 ? "" : ", ") + (java.lang.String) values[vv]; }

}

else {

REF_TEKLIF_NO = (java.lang.String) value;

}