added check to verify not to add void APC

dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/dump/ResultMapper.java

@@ -426,10 +426,15 @@ public class ResultMapper implements Serializable {
 		Optional<Field<String>> oPca = Optional.ofNullable(i.getProcessingchargeamount());
 		Optional<Field<String>> oPcc = Optional.ofNullable(i.getProcessingchargecurrency());
 		if (oPca.isPresent() && oPcc.isPresent()) {
-			APC apc = new APC();
-			apc.setCurrency(oPcc.get().getValue());
-			apc.setAmount(oPca.get().getValue());
-			instance.setArticleprocessingcharge(apc);
+			Field<String> pca = oPca.get();
+			Field<String> pcc = oPcc.get();
+			if(!pca.getValue().trim().equals("") && !pcc.getValue().trim().equals("")){
+				APC apc = new APC();
+				apc.setCurrency(oPcc.get().getValue());
+				apc.setAmount(oPca.get().getValue());
+				instance.setArticleprocessingcharge(apc);
+			}
+
 		}
 
 	}