Description of the false positive
It tells me that the class extends from the OutputStream and implements write, but does not override write(byte[],int,int).
But a few lines below you can see, that the method is overridden:
public void write(@NotNull byte[] b, int off, int len) throws IOException {
I think it just doesn't recognize it because of the @NotNull annotation.
URL to the alert on the project page on LGTM.com
https://lgtm.com/projects/g/CloudNetService/CloudNet-v3/rev/pr-59fec0855f9b28083090ba30f93da3f14acfcd27