Fix some warnings.

src/main/java/edu/hm/hafner/coverage/FileNode.java

@@ -145,11 +145,11 @@ private void mergeCounters(final FileNode otherFile) {
         var lineCoverage = new CoverageBuilder().withMetric(Metric.LINE).withCovered(0).withMissed(0);
         var branchCoverage = new CoverageBuilder().withMetric(Metric.BRANCH).withCovered(0).withMissed(0);
         for (int line : lines) {
-            int leftCovered = coveredPerLine.get(line);
-            int leftMissed = missedPerLine.get(line);
+            int leftCovered = coveredPerLine.getOrDefault(line, 0);
+            int leftMissed = missedPerLine.getOrDefault(line, 0);
             int leftTotal = leftCovered + leftMissed;
-            int rightCovered = otherFile.coveredPerLine.get(line);
-            int rightMissed = otherFile.missedPerLine.get(line);
+            int rightCovered = otherFile.coveredPerLine.getOrDefault(line, 0);
+            int rightMissed = otherFile.missedPerLine.getOrDefault(line, 0);
             int rightTotal = rightCovered + rightMissed;
 
             if (leftTotal != rightTotal) {
@@ -580,7 +580,7 @@ private NavigableSet<Integer> filterLines(final Predicate<Integer> predicate) {
      * @return the aggregated LineRanges that have no line coverage
      */
     public LineRangeList getMissedLineRanges() {
-        LineRangeList lineRanges = new LineRangeList();
+        var lineRanges = new LineRangeList();
 
         var missedLines = getMissedLines();
         if (missedLines.isEmpty()) {

src/main/java/edu/hm/hafner/coverage/Node.java

@@ -384,6 +384,22 @@ public List<Node> getAll(final Metric searchMetric) {
         return childNodes;
     }
 
+    private <T extends Node> List<T> getAll(final Metric metric1, final Function<Node, T> cast) {
+        return getAll(metric1).stream().map(cast).collect(Collectors.toList());
+    }
+
+    public List<FileNode> getAllFileNodes() {
+        return getAll(Metric.FILE, FileNode.class::cast);
+    }
+
+    public List<ClassNode> getAllClassNodes() {
+        return getAll(Metric.CLASS, ClassNode.class::cast);
+    }
+
+    public List<MethodNode> getAllMethodNodes() {
+        return getAll(Metric.METHOD, MethodNode.class::cast);
+    }
+
     /**
      * Finds the metric with the given name starting from this node.
      *
@@ -481,22 +497,6 @@ public Set<String> getFiles() {
         return children.stream().map(Node::getFiles).flatMap(Collection::stream).collect(Collectors.toSet());
     }
 
-    public List<FileNode> getAllFileNodes() {
-        return getAll(Metric.FILE, FileNode.class::cast);
-    }
-
-    public List<ClassNode> getAllClassNodes() {
-        return getAll(Metric.CLASS, ClassNode.class::cast);
-    }
-
-    public List<MethodNode> getAllMethodNodes() {
-        return getAll(Metric.METHOD, MethodNode.class::cast);
-    }
-
-    private <T extends Node> List<T> getAll(final Metric metric1, final Function<Node, T> cast) {
-        return getAll(metric1).stream().map(cast).collect(Collectors.toList());
-    }
-
     /**
      * Finds the metric with the given hash code starting from this node.
      *
@@ -649,11 +649,11 @@ public void mapTests(final List<ClassNode> testClassNodes) {
     private void mapTestClass(final ClassNode testClassNode) {
         findPackage(testClassNode.getPackageName())
                 .ifPresent(packageNode -> packageNode.getAllClassNodes().stream()
-                        .filter(classNode -> matches(testClassNode, classNode))
+                        .filter(classNode -> isTargetOfTest(classNode, testClassNode))
                         .forEach(classNode -> classNode.addTestCases(testClassNode.getTestCases())));
     }
 
-    private boolean matches(final ClassNode testClassNode, final ClassNode classNode) {
+    private boolean isTargetOfTest(final ClassNode classNode, final ClassNode testClassNode) {
         return classNode.getName().endsWith(createTargetClassName(testClassNode));
     }
 

src/main/java/edu/hm/hafner/coverage/PackageNode.java

@@ -41,6 +41,7 @@ public PackageNode(@CheckForNull final String name) {
         super(Metric.PACKAGE, normalizePackageName(name));
     }
 
+    @SuppressWarnings("CanIgnoreReturnValueSuggester")
     static PackageNode appendPackage(final PackageNode localChild, final PackageNode localParent) {
         localParent.addChild(localChild);
         return localParent;

src/main/java/edu/hm/hafner/coverage/parser/JacocoParser.java

@@ -13,6 +13,8 @@
 
 import org.apache.commons.lang3.StringUtils;
 
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
+
 import edu.hm.hafner.coverage.ClassNode;
 import edu.hm.hafner.coverage.Coverage.CoverageBuilder;
 import edu.hm.hafner.coverage.CoverageParser;
@@ -90,6 +92,7 @@ protected ModuleNode parseReport(final Reader reader, final FilteredLog log) {
         }
     }
 
+    @CanIgnoreReturnValue
     private ModuleNode readModule(final XMLEventReader reader, final ModuleNode module)
             throws XMLStreamException {
         while (reader.hasNext()) {
@@ -123,6 +126,7 @@ private boolean isModuleEnd(final EndElement endElement) {
         return REPORT.equals(endElement.getName()) || GROUP.equals(endElement.getName());
     }
 
+    @CanIgnoreReturnValue
     private PackageNode readPackage(final XMLEventReader reader,
             final ModuleNode root, final StartElement startElement) throws XMLStreamException {
         var packageName = getValueOf(startElement, NAME);
@@ -152,6 +156,7 @@ else if (event.isEndElement()) {
         throw createEofException();
     }
 
+    @CanIgnoreReturnValue
     private Node readClass(final XMLEventReader reader, final PackageNode packageNode,
             final String packageName, final StartElement startElement) throws XMLStreamException {
         Optional<String> possibleFileName = getOptionalValueOf(startElement, SOURCE_FILE_NAME);
@@ -192,6 +197,7 @@ private TreeString internPath(final String packageName, final String fileName) {
         return getTreeStringBuilder().intern(PATH_UTIL.getRelativePath(Paths.get(packageName, fileName)));
     }
 
+    @CanIgnoreReturnValue
     private Node readSourceFile(final XMLEventReader reader, final PackageNode packageNode,
             final String packageName, final StartElement startElement) throws XMLStreamException {
         String fileName = getValueOf(startElement, NAME);
@@ -238,6 +244,7 @@ private void readLine(final FileNode fileNode, final StartElement startElement)
         fileNode.addCounters(lineNumber, covered, missed);
     }
 
+    @CanIgnoreReturnValue
     private Node readMethod(final XMLEventReader reader, final ClassNode classNode,
             final StartElement startElement) throws XMLStreamException {
         String methodName = getValueOf(startElement, NAME);