replace default string representation of Iterable fields with pipe-de…

…limited format

affects application/csv, application/kvp+json, and text/csv return types
fixes #375

service/src/main/java/gov/nasa/pds/api/registry/model/WyriwygBusinessObject.java

@@ -2,11 +2,15 @@
 
 import java.net.URL;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
 import java.util.TreeSet;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
 import org.opensearch.search.SearchHit;
 import org.opensearch.search.SearchHits;
 import org.slf4j.Logger;
@@ -111,7 +115,7 @@ public int setResponse(SearchHits hits, Summary summary, List<String> fields) {
         WyriwygProductKeyValuePair kvp = new WyriwygProductKeyValuePair();
         try {
           kvp.setKey(SearchUtil.openPropertyToJsonProperty(pair.getKey()));
-          kvp.setValue(String.valueOf(pair.getValue()));
+          kvp.setValue(getStringValueOf(pair.getValue()));
           product.addKeyValuePairsItem(kvp);
         } catch (UnsupportedSearchProperty e) {
           log.warn("openSearch property " + pair.getKey() + " is not supported, ignored");
@@ -125,4 +129,21 @@ public int setResponse(SearchHits hits, Summary summary, List<String> fields) {
     this.products = products;
     return (int) (hits.getTotalHits().value);
   }
+
+  private String getStringValueOf(Object o) {
+    String valueOf;
+    if (o instanceof Iterable) {
+      List<String> stringRepresentations = new ArrayList<>();
+      for (Object el : (Iterable<Object>) o ) {
+        stringRepresentations.add(String.valueOf(el));
+      }
+
+      String delimiter = "|";
+      valueOf = String.join(delimiter, stringRepresentations);
+    } else {
+      valueOf = String.valueOf(o);
+    }
+
+    return valueOf;
+  }
 }