Ignore kubeconfig changes where the config file is empty or deleted

I'm not convinced this is doing much to address
redhat-developer/intellij-kubernetes#640.
In practice, the first few times I attempt to switch namespaces,
the tree collapses, regardless of if I use this PR or the existing code.
After that, I can occasionally switch namespaces without the tree
collapsing.

See redhat-developer#190.

Signed-off-by: David Thompson <[email protected]>

src/main/java/com/redhat/devtools/intellij/common/utils/ConfigWatcher.java

@@ -16,6 +16,7 @@
 
 import java.io.IOException;
 import java.nio.file.FileSystems;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.nio.file.StandardWatchEventKinds;
@@ -66,7 +67,8 @@ private void runOnConfigChange(Runnable runnable) {
             while ((key = service.take()) != null) {
                 key.pollEvents().stream()
                         .filter(this::isConfigPath)
-                        .forEach((Void) -> runnable.run());
+                        .filter(this::isValid)
+                        .forEach(Void -> runnable.run());
                 key.reset();
             }
         } catch (IOException | InterruptedException e) {
@@ -95,6 +97,26 @@ protected boolean isConfigPath(WatchEvent<?> event) {
         return path.equals(config);
     }
 
+	/**
+	 * Returns {@code true} if the path (to the kube config file) in the given event
+	 * <ul>
+	 *     <li>exists and</li>
+	 *     <li>is not empty</li>
+	 * </ul>
+	 *
+	 * @param event the WatchEvent to get the path to the kube config from
+	 * @return returns true if the kube config that the event points to exists and is not empty
+	 */
+	protected boolean isValid(WatchEvent<?> event) {
+		Path path = getWatchedPath().resolve((Path) event.context());
+		try {
+			return Files.exists(path) && Files.size(path) > 0;
+		} catch (IOException e) {
+			// do nothing
+		}
+		return true;
+	}
+
     private Path getWatchedPath() {
         return config.getParent();
     }