Log a warning if a DockerCloud name is blank

Do not break existing usage of blank names, but warn in the log file
that blank names are no longer supported after Jenkins 2.402.

The Jenkins 2.421 cloud creation UI will not allow a blank name, but
earlier versions may have allowed it.

Assert the log message for blank or name cloud name

src/main/java/com/nirima/jenkins/plugins/docker/DockerCloud.java

@@ -138,6 +138,9 @@ public DockerCloud(String name, DockerAPI dockerApi, List<DockerTemplate> templa
         super(name);
         this.dockerApi = dockerApi;
         this.templates = templates;
+        if (name == null || name.isBlank()) {
+            LOGGER.warn("Docker cloud requires a non-blank name after Jenkins 2.402");
+        }
     }
 
     @Deprecated

src/test/java/com/nirima/jenkins/plugins/docker/DockerCloudTest.java

@@ -18,12 +18,17 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.logging.Level;
+import org.hamcrest.MatcherAssert;
+import org.hamcrest.core.IsIterableContaining;
 import org.jenkinsci.plugins.docker.commons.credentials.DockerServerCredentials;
 import org.jenkinsci.plugins.docker.commons.credentials.DockerServerEndpoint;
 import org.junit.Assert;
 import org.junit.Rule;
 import org.junit.Test;
+import org.jvnet.hudson.test.Issue;
 import org.jvnet.hudson.test.JenkinsRule;
+import org.jvnet.hudson.test.LoggerRule;
 
 /**
  * @author Kanstantsin Shautsou
@@ -33,6 +38,9 @@ public class DockerCloudTest {
     @Rule
     public JenkinsRule jenkins = new JenkinsRule();
 
+    @Rule
+    public LoggerRule lr = new LoggerRule();
+
     @SuppressWarnings("unused")
     @Test
     public void testConstructor_0_10_2() {
@@ -48,6 +56,28 @@ public void testConstructor_0_10_2() {
                 null); // dockerHostname
     }
 
+    private static final String LOG_MESSAGE = "Docker cloud requires a non-blank name after Jenkins 2.402";
+
+    @Issue("JENKINS-70729") // Warn if cloud name is empty
+    @Test
+    public void testConstructorWithEmptyName() {
+        lr.record(DockerCloud.class.getName(), Level.ALL).capture(16);
+        DockerCloud cloud =
+                new DockerCloud("", new DockerAPI(new DockerServerEndpoint("uri", "credentialsId")), List.of());
+        Assert.assertEquals(cloud.getDisplayName(), "");
+        MatcherAssert.assertThat(lr.getMessages(), IsIterableContaining.hasItem(LOG_MESSAGE));
+    }
+
+    @Issue("JENKINS-70729") // Warn if cloud name is null
+    @Test
+    public void testConstructorWithNullName() {
+        lr.record(DockerCloud.class.getName(), Level.ALL).capture(16);
+        DockerCloud cloud =
+                new DockerCloud(null, new DockerAPI(new DockerServerEndpoint("uri", "credentialsId")), List.of());
+        Assert.assertEquals(cloud.getDisplayName(), null);
+        MatcherAssert.assertThat(lr.getMessages(), IsIterableContaining.hasItem(LOG_MESSAGE));
+    }
+
     @Test
     public void globalConfigRoundtrip() throws Exception {