Question: I am trying to delete the nodes that has a relationship to each other node if the relationship exist. If the relationship doesnt exist delete the first node. Example:
I am using UNWIND because that is the data provided by the user.

```
UNWIND [{name:'John'}] as rows
IF EXISTS(u:Person)-[r:OWNS]->(c:Car), THEN
MATCH (u:Person)-[r:OWNS]->(c:Car)
WHERE u.user_name = rows.name
DETACH DELETE u,c
OTHERWISE
MATCH (u:Person)
WHERE u.user_name = rows.name
DETACH DELETE u

```

I tried using apoc.do.when however they dont allow EXISTS(u:User)-[r:OWNS]->(c:Car) as a conditional statement.

Answer: 
I have faced the same issue. Don't pacnic. Open Windows `cmd` or Ubuntu/MacOS/Linux `terminal` and run `flutter upgrade -v` . 

It takes time to download and sometimes if failed error doesn't appear in IDE.
In terminal/cmd you can see the progress.

Restart your IDE once the upgrade finishes.
i slove that error reinstall the Dart SDK using [Chocolatey](https://chocolatey.org/install).

> 
> Important: These commands require administrator rights. Here’s one way to open a Command Prompt window that has admin rights:
> 
> 
> 

Press Windows+R to open the Run window.
Type cmd into the box.

> 
> Press Ctrl+Shift+Enter.
> 
> 
> 

To install the Dart SDK:

> 
> `choco install dart-sdk`
> 
> 
> 

To upgrade the Dart SDK:

> 
> `choco upgrade dart-sdk`
> 
> 
> 

By default, the SDK is installed at C:\tools\dart-sdk. You can change that location by setting the ChocolateyToolsLocation environment variable to your chosen installation directory.

If you can’t use the Dart SDK executables, add the SDK location to your PATH:

1. In the Windows search box, type env.
2. Click Edit the system environment variables.
3. Click Environment Variables….
4. In the user variable section, select Path and click Edit….
5. Click New, and enter the path to the dart-sdk directory.
6. In each window that you just opened, click Apply or OK to dismiss it and apply the path change.