fix: Yaml实例加载时基本类型设置异常

src/main/java/com/serliunx/ddns/core/factory/YamlFileInstanceFactory.java

@@ -93,6 +93,7 @@ public class YamlFileInstanceFactory extends FileInstanceFactory {
                     f.set(instance, Enum.valueOf((Class<? extends Enum>) clazz, (String) value));
                     continue;
                 }
+                if (value != null)
                     f.set(instance, value);
             } catch (IllegalAccessException e) {
                 throw new RuntimeException(e);