public static boolean isJsonValid(String schemaText, String jsonText) throws IOException {
      return isJsonValid(schemaText, jsonText, null);
   }
@Test
   void testValidateJsonSuccessWithNull() {
      boolean valid = false;
      String schemaText = null;
      String jsonText = "{\"name\": \"307\", \"model\": null, \"year\": 2003}";

      try {
         // Load schema from file.
         schemaText = FileUtils
               .readFileToString(new File("target/test-classes/io/github/microcks/util/openapi/car-schema.json"));
         // Validate Json according schema.
         valid = OpenAPISchemaValidator.isJsonValid(schemaText, jsonText);
      } catch (Exception e) {
         fail("Exception should not be thrown");
      }

      // Assert Json object is valid.
      assertTrue(valid);
   }