fix: 修复在redis缓存下集合为空数据组的情况

 package org.thingsboard.server.common.data.yunteng.core.cache;
+
 import org.springframework.cache.Cache;
 import org.springframework.cache.CacheManager;
 import org.springframework.stereotype.Component;
 import org.thingsboard.server.common.data.yunteng.constant.FastIotConstants;
+
+import java.util.Collection;
 import java.util.Objects;
 import java.util.Optional;
 
@@ -49,17 +52,25 @@ public class CacheUtils {
     }
   }
 
-  @SuppressWarnings("unchecked")
   public <T> Optional<T> get(String key) {
     return Optional.ofNullable(cacheManager.getCache(COMMON_STORE_AREA))
         .map(cache -> Objects.requireNonNull(cache).get(key))
-        .map(v -> (T) v.get());
+        .map(this::getValue);
   }
 
-  @SuppressWarnings("unchecked")
   public <T> Optional<T> get(String cacheName, String key) {
     return Optional.ofNullable(cacheManager.getCache(cacheName))
         .map(cache -> Objects.requireNonNull(cache).get(key))
-        .map(v -> (T) v.get());
+        .map(this::getValue);
+  }
+
+  private <T> T getValue(Cache.ValueWrapper v) {
+    if (v.get() instanceof Collection) {
+      if (((Collection<?>) Objects.requireNonNull(v.get())).size()
+          == FastIotConstants.MagicNumber.ZERO) {
+        return null;
+      }
+    }
+    return (T) v.get();
   }
 }