feat(api, spi, storage): transformer fix

Signed-off-by: Sascha Isele <[email protected]>

spi/common/json-ld-spi/src/main/java/org/eclipse/edc/jsonld/spi/transformer/AbstractJsonLdTransformer.java

@@ -285,7 +285,7 @@ protected String transformString(JsonValue value, TransformerContext context) {
 
     /**
      * Transforms a JsonValue to a list of strings. If the value parameter is not of type JsonString, JsonObject or JsonArray,
-     * a problem is reported to the context.
+     * a problem is reported to the context and an empty list is returned.
      *
      * @param value   the value to transform
      * @param context the transformer context
@@ -334,7 +334,7 @@ protected List<String> transformIdStringArray(JsonValue value, TransformerContex
                     .expected(ARRAY)
                     .report();
         }
-        return null;
+        return result;
     }
 
     /**