Issue #359: fix NPE when parsing gc log file without any events

IT/src/test/java/com/microsoft/gctoolkit/integration/DirtyDataIntegrationTest.java

@@ -0,0 +1,52 @@
+package com.microsoft.gctoolkit.integration;
+
+import com.microsoft.gctoolkit.GCToolKit;
+import com.microsoft.gctoolkit.integration.aggregation.CollectionCycleCountsSummary;
+import com.microsoft.gctoolkit.integration.io.TestLogFile;
+import com.microsoft.gctoolkit.io.GCLogFile;
+import com.microsoft.gctoolkit.io.SingleGCLogFile;
+import com.microsoft.gctoolkit.parser.GenerationalHeapParser;
+import com.microsoft.gctoolkit.vertx.VertxDataSourceChannel;
+import com.microsoft.gctoolkit.vertx.VertxJVMEventChannel;
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.nio.file.Path;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+@Tag("classPath")
+public class DirtyDataIntegrationTest {
+
+  /**
+   * Test a GC log file that contains only the header but no actual events
+   */
+  @Test
+  public void testNoEventLog() {
+    Path path = new TestLogFile("streaming/gc_no_event.log").getFile().toPath();
+    assertThrows(IllegalStateException.class, () -> analyze(path.toString()));
+  }
+
+  /**
+   * Test an empty file that contains nothing
+   */
+  @Test
+  public void testEmptyFile() {
+    Path path = new TestLogFile("streaming/gc_empty.log").getFile().toPath();
+    assertThrows(IllegalStateException.class, () -> analyze(path.toString()));
+  }
+
+  public void analyze(String gcLogFile) throws IOException {
+    GCLogFile logFile = new SingleGCLogFile(Path.of(gcLogFile));
+    GCToolKit gcToolKit = new GCToolKit();
+
+    gcToolKit.loadDataSourceChannel(new VertxDataSourceChannel());
+    gcToolKit.loadJVMEventChannel(new VertxJVMEventChannel());
+    gcToolKit.loadDataSourceParser(new GenerationalHeapParser());
+
+    gcToolKit.loadAggregation(new CollectionCycleCountsSummary());
+
+    gcToolKit.analyze(logFile);
+  }
+}

parser/src/main/java/com/microsoft/gctoolkit/parser/GCLogParser.java

@@ -53,6 +53,10 @@ public GCLogParser() {}
     public void diary(Diary diary) {
         this.diary = diary;
         this.clock = diary.getTimeOfFirstEvent();
+        if (this.clock == null) {
+            LOGGER.log(Level.SEVERE, "Time of first event is null, are there any events presented in the log file?");
+            throw new IllegalStateException("Missing log events");
+        }
     }
 
     /**