Do not discard auth command if no args

CHANGELOG.md

@@ -6,6 +6,7 @@
 * Fix #3745: the client will throw better exceptions when a namespace is not discernible for an operation
 * Fix #4106: removed listing from projectrequests
 * Fix #4081: moving Versionable.withResourceVersion to a method on WatchAndWaitable and removing Waitable from the return type
+* Fix #3733: The authentication command from the .kube/config won't be discarded if no arguments are specified
 
 #### Improvements
 * Remove `setIntVal`, `setStrVal`, `setKind` setters from `IntOrString` class to avoid invalid combinations

kubernetes-client-api/src/main/java/io/fabric8/kubernetes/client/Config.java

@@ -766,9 +766,10 @@ protected static List<String> getAuthenticatorCommandFromExecConfig(ExecConfig e
     List<String> argv = new ArrayList<>(Utils.getCommandPlatformPrefix());
     command = getCommandWithFullyQualifiedPath(command, systemPathValue);
     List<String> args = exec.getArgs();
-    if (args != null) {
-      argv.add(command + " " + String.join(" ", args));
+    if (args != null && !args.isEmpty()) {
+      command += " " + String.join(" ", args);
     }
+    argv.add(command);
     return argv;
   }
 

kubernetes-client-api/src/test/java/io/fabric8/kubernetes/client/ConfigTest.java

@@ -582,6 +582,30 @@ void testGetAuthenticatorCommandFromExecConfig() throws IOException {
     assertEquals("api-eks.example.com", commandParts.get(6));
   }
 
+  @Test
+  void testGetAuthenticatorCommandFromExecConfigNullArgs() throws IOException {
+    // Given
+    File commandFolder = Files.createTempDirectory("test").toFile();
+    File commandFile = new File(commandFolder, "gke-gcloud-auth-plugin");
+    String systemPathValue = getTestPathValue(commandFolder);
+    ExecConfig execConfigNoArgs = new ExecConfigBuilder()
+        .withApiVersion("client.authentication.k8s.io/v1alpha1")
+        .withCommand(commandFile.getPath())
+        .build();
+    // Simulate "user.exec.args: null" like e.g. in the configuration for the gke-gcloud-auth-plugin.
+    execConfigNoArgs.setArgs(null);
+
+    // When
+    List<String> processBuilderArgs = Config.getAuthenticatorCommandFromExecConfig(
+        execConfigNoArgs, null, systemPathValue);
+
+    // Then
+    assertNotNull(processBuilderArgs);
+    assertEquals(3, processBuilderArgs.size());
+    assertPlatformPrefixes(processBuilderArgs);
+    assertEquals(commandFile.getPath(), processBuilderArgs.get(2));
+  }
+
   private void assertPlatformPrefixes(List<String> processBuilderArgs) {
     List<String> platformArgsExpected = Utils.getCommandPlatformPrefix();
     assertEquals(platformArgsExpected.get(0), processBuilderArgs.get(0));