fix

src/main/java/cn/axzo/pokonyan/config/mybatisplus/type/SetTypeHandler.java

@@ -58,7 +58,7 @@ public class SetTypeHandler extends BaseTypeHandler<Set<String>> {
         return Splitter.on(",")
                 .omitEmptyStrings()
                 .trimResults()
-                .splitToList(Optional.of(dbValue).orElse(StringUtils.EMPTY))
+                .splitToList(Optional.ofNullable(dbValue).orElse(StringUtils.EMPTY))
                 .stream()
                 .collect(Collectors.toSet());
     }