How can I get the "SOFPART" attribute value of the document type object in the promotion?

How can I get the "SOFPART" attribute value of the document type object in the promotion?

SOFPART contains multiple string values

I wrote a code to deal with this situation, but the attribute value is empty. Where am I making a mistake?

CODE:

try {
 wt.maturity.PromotionNotice pn = (wt.maturity.PromotionNotice) primaryBusinessObject;
 wt.fc.QueryResult qr = wt.maturity.MaturityHelper.service.getBaselineItems(pn);
 
 while (qr.hasMoreElements()) {
 java.lang.Object obj=(java.lang.Object)qr.nextElement();

 if (obj instanceof wt.doc.WTDocument) {
 wt.doc.WTDocument wtdoc = (wt.doc.WTDocument) obj;
 wt.content.ContentHolder contentHolder = wt.content.ContentHelper.service.getContents(wtdoc);
 wt.content.ContentItem item = wt.content.ContentHelper.getPrimary((wt.content.FormatContentHolder) contentHolder);
 com.ptc.core.lwc.server.PersistableAdapter persistableAdapter = new com.ptc.core.lwc.server.PersistableAdapter(wtdoc, null, java.util.Locale.getDefault(), new com.ptc.core.meta.common.UpdateOperationIdentifier());
 persistableAdapter.load("SOFPART");
 SOFPART = (java.lang.String) persistableAdapter.get("SOFPART");
 }
 }
} catch (Exception wte) {
 wte.printStackTrace();
}