Check null before close connection

components/device-mgt/org.wso2.carbon.device.mgt.core/src/main/java/org/wso2/carbon/device/mgt/core/operation/mgt/dao/OperationManagementDAOFactory.java

@@ -94,6 +94,7 @@ public class OperationManagementDAOFactory {
     public static void closeConnection() throws OperationManagementDAOException {
 
         Connection con = currentConnection.get();
+        if (con != null) {
             try {
                 con.close();
             } catch (SQLException e) {
@@ -101,6 +102,7 @@ public class OperationManagementDAOFactory {
             }
             currentConnection.remove();
         }
+    }
 
     public static void commitTransaction() throws OperationManagementDAOException {
         try {