fix: handle null FlowExecution in PipelineLogExtractor (#97)

* fix: handle null FlowExecution in PipelineLogExtractor

WorkflowRun.getExecution() can return null when the pipeline execution
has not yet started, was interrupted very early, or has been cleaned up.
Without this check, FlowGraphWalker throws a NullPointerException.

Fall back to the overall build log when execution is null, which is
consistent with the existing fallback behavior for non-pipeline builds.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: add PipelineLogExtractor tests for null execution fallback

Add test coverage for the null FlowExecution guard:
- testNullFlowExecutionFallsBackToBuildLog: verifies that a
  WorkflowRun with null execution falls back to run.getLog()
  without throwing NullPointerException
- testNonPipelineBuildFallsBackToBuildLog: verifies that non-pipeline
  builds (FreeStyleBuild) also fall back correctly

Add mockito-core as a test dependency to enable mocking WorkflowRun.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: lidiams96

pom.xml

@@ -144,6 +144,12 @@
       <scope>test</scope>
     </dependency>
 
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+
     <dependency>
       <groupId>dev.langchain4j</groupId>
       <artifactId>langchain4j</artifactId>

src/main/java/io/jenkins/plugins/explain_error/PipelineLogExtractor.java

@@ -101,6 +101,10 @@ public List<String> getFailedStepLog() throws IOException {
 
         if (this.run instanceof WorkflowRun) {
             FlowExecution execution = ((WorkflowRun) this.run).getExecution();
+            if (execution == null) {
+                setUrl("0");
+                return run.getLog(maxLines);
+            }
 
             FlowGraphWalker walker = new FlowGraphWalker(execution);
             for (FlowNode node : walker) {

src/test/java/io/jenkins/plugins/explain_error/PipelineLogExtractorTest.java

@@ -0,0 +1,62 @@
+package io.jenkins.plugins.explain_error;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import hudson.model.FreeStyleBuild;
+import hudson.model.FreeStyleProject;
+import java.util.List;
+import org.jenkinsci.plugins.workflow.job.WorkflowRun;
+import org.junit.jupiter.api.Test;
+import org.jvnet.hudson.test.JenkinsRule;
+import org.jvnet.hudson.test.junit.jupiter.WithJenkins;
+
+@WithJenkins
+class PipelineLogExtractorTest {
+
+    @Test
+    void testNullFlowExecutionFallsBackToBuildLog(JenkinsRule jenkins) throws Exception {
+        // Create a mock WorkflowRun where getExecution() returns null
+        WorkflowRun mockRun = mock(WorkflowRun.class);
+        when(mockRun.getExecution()).thenReturn(null);
+        when(mockRun.getLog(100)).thenReturn(List.of("Build started", "ERROR: Something failed"));
+        when(mockRun.getUrl()).thenReturn("job/test/1/");
+
+        PipelineLogExtractor extractor = new PipelineLogExtractor(mockRun, 100);
+
+        // Should not throw NullPointerException
+        List<String> logLines = assertDoesNotThrow(() -> extractor.getFailedStepLog());
+
+        // Should fall back to build log
+        assertNotNull(logLines);
+        assertEquals(2, logLines.size());
+        assertEquals("ERROR: Something failed", logLines.get(1));
+
+        // URL should be set (either console or stages depending on plugin availability)
+        String url = extractor.getUrl();
+        assertNotNull(url, "URL should not be null after getFailedStepLog()");
+        assertTrue(url.contains("job/test/1/"), "URL should reference the build");
+    }
+
+    @Test
+    void testNonPipelineBuildFallsBackToBuildLog(JenkinsRule jenkins) throws Exception {
+        // FreeStyleBuild is not a WorkflowRun, so it should skip the pipeline path entirely
+        FreeStyleProject project = jenkins.createFreeStyleProject();
+        FreeStyleBuild build = jenkins.buildAndAssertSuccess(project);
+
+        PipelineLogExtractor extractor = new PipelineLogExtractor(build, 100);
+        List<String> logLines = extractor.getFailedStepLog();
+
+        assertNotNull(logLines);
+        assertFalse(logLines.isEmpty());
+
+        String url = extractor.getUrl();
+        assertNotNull(url);
+        assertTrue(url.contains(build.getUrl()), "URL should reference the build");
+    }
+}