Replace StringUtils with our implementation

+/**
+ * Copyright © 2016-2021 The Thingsboard Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.thingsboard.server.common.data;
+
+public class StringUtils {
+
+    public static boolean isEmpty(String source) {
+        return source == null || source.isEmpty();
+    }
+
+    public static boolean isNotEmpty(String source) {
+        return source != null && !source.isEmpty();
+    }
+}

@@ -16,7 +16,7 @@
 package org.thingsboard.server.common.data.event;
 
 import lombok.Data;
-import org.eclipse.leshan.core.util.StringUtils;
+import org.thingsboard.server.common.data.StringUtils;
 
 @Data
 public abstract class DebugEvent implements EventFilter {

@@ -16,7 +16,7 @@
 package org.thingsboard.server.common.data.event;
 
 import lombok.Data;
-import org.eclipse.leshan.core.util.StringUtils;
+import org.thingsboard.server.common.data.StringUtils;
 
 @Data
 public class ErrorEventFilter implements EventFilter {

@@ -16,7 +16,7 @@
 package org.thingsboard.server.common.data.event;
 
 import lombok.Data;
-import org.eclipse.leshan.core.util.StringUtils;
+import org.thingsboard.server.common.data.StringUtils;
 
 @Data
 public class LifeCycleEventFilter implements EventFilter {

@@ -16,7 +16,7 @@
 package org.thingsboard.server.common.data.event;
 
 import lombok.Data;
-import org.eclipse.leshan.core.util.StringUtils;
+import org.thingsboard.server.common.data.StringUtils;
 
 @Data
 public class StatisticsEventFilter implements EventFilter {