Minor changes to registry serialization

core/src/main/java/org/polypheny/db/algebra/polyalg/PolyAlgDeclaration.java

@@ -217,6 +217,9 @@ public ObjectNode serialize( ObjectMapper mapper ) {
         for ( Parameter p : posParams ) {
             posArr.add( p.serialize( mapper ) );
         }
+        if ( !posArr.isEmpty() && canUnpackValues() ) {
+            ((ObjectNode) posArr.get( 0 )).put( "canUnpackValues", true);
+        }
         node.set( "posParams", posArr );
 
         ArrayNode kwArr = mapper.createArrayNode();
@@ -308,6 +311,7 @@ public ObjectNode serialize( ObjectMapper mapper ) {
             node.put( "requiresAlias", requiresAlias );
             if ( !isPositional() ) {
                 node.set( "defaultValue", defaultValue.serializeWrapped( null, List.of(), mapper ) );
+                node.put( "defaultPolyAlg", defaultValue.toPolyAlg( null, List.of() ) );
             }
             node.put( "isEnum", type.isEnum() );
 

core/src/main/java/org/polypheny/db/algebra/polyalg/PolyAlgUtils.java

@@ -115,12 +115,16 @@ private static boolean isCastWithSameName( String exp, String alias ) {
     /**
      * Joins the values for a multivalued attribute into a single string.
      * If values contains more than one element, the returned string is surrounded with brackets to represent a list.
+     * An empty list is indicated with {@code "[]"}.
      *
      * @param values the values to be joined
      * @param omitBrackets whether the surrounding brackets in the case of multiple values should be omitted
      * @return a string either representing a list containing all entries of values or a single value if values is of size 1
      */
     public static String joinMultiValued( List<String> values, boolean omitBrackets ) {
+        if ( values.isEmpty() ) {
+            return "[]";
+        }
         String str = String.join( ", ", values );
         return (omitBrackets || values.size() <= 1) ? str : "[" + str + "]";
     }