handle "/" in exist

other/java/client/src/main/java/seaweedfs/client/FilerClient.java

@@ -128,7 +128,14 @@ public class FilerClient extends FilerGrpcClient {
 
     public boolean exists(String path){
         File pathFile = new File(path);
-        return lookupEntry(pathFile.getParent(), pathFile.getName()) != null;
+        String parent = pathFile.getParent();
+        String entryName = pathFile.getName();
+        if(parent == null) {
+            parent = path;
+            entryName  ="";
+        }
+        return lookupEntry(parent, entryName) != null;
+
     }
 
     public boolean rm(String path, boolean isRecursive, boolean ignoreRecusiveError) {

other/java/client/src/test/java/seaweedfs/client/SeaweedFilerTest.java

@@ -25,5 +25,8 @@ public class SeaweedFilerTest {
         if(filerClient.exists("/new_folder/new_empty_file")){
             System.out.println("/new_folder/new_empty_file should not exists");
         }
+        if(!filerClient.exists("/")){
+            System.out.println("/ should exists");
+        }
     }
 }