Add @nullable annotations throughout the codebase

Author: Vincent Potucek

api/maven-api-core/src/main/java/org/apache/maven/api/services/Sources.java

@@ -175,11 +175,13 @@ static class ResolvedPathSource extends PathSource implements ModelSource {
         }
 
         @Override
+        @Nullable
         public Path getPath() {
             return null;
         }
 
         @Override
+        @Nullable
         public Source resolve(String relative) {
             return null;
         }

api/maven-api-core/src/main/java/org/apache/maven/api/services/xml/XmlReaderRequest.java

@@ -207,6 +207,7 @@ public Path getRootDirectory() {
             }
 
             @Override
+            @Nullable
             public URL getURL() {
                 return null;
             }

api/maven-api-xml/src/main/java/org/apache/maven/api/xml/XmlNode.java

@@ -473,11 +473,13 @@ private record Impl(
             }
 
             @Override
+            @Nullable
             public String attribute(@Nonnull String name) {
                 return attributes.get(name);
             }
 
             @Override
+            @Nullable
             public XmlNode child(String name) {
                 if (name != null) {
                     ListIterator<XmlNode> it = children.listIterator(children.size());

compat/maven-artifact/pom.xml

@@ -41,6 +41,10 @@ under the License.
       <artifactId>junit-jupiter-params</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.apache.maven</groupId>
+      <artifactId>maven-api-annotations</artifactId>
+    </dependency>
   </dependencies>
 
   <build>

compat/maven-artifact/src/main/java/org/apache/maven/artifact/versioning/VersionRange.java

@@ -26,6 +26,7 @@
 import java.util.Objects;
 import java.util.WeakHashMap;
 
+import org.apache.maven.api.annotations.Nullable;
 import org.apache.maven.artifact.Artifact;
 import org.apache.maven.artifact.DefaultArtifact;
 
@@ -92,6 +93,7 @@ public VersionRange cloneOf() {
      * @return a new {@link VersionRange} object that represents the spec
      * @throws InvalidVersionSpecificationException if invalid version specification
      */
+    @Nullable
     public static VersionRange createFromVersionSpec(String spec) throws InvalidVersionSpecificationException {
         if (spec == null) {
             return null;
@@ -202,6 +204,7 @@ private static Restriction parseRestriction(String spec) throws InvalidVersionSp
         return restriction;
     }
 
+    @Nullable
     public static VersionRange createFromVersion(String version) {
         if (DefaultArtifact.empty(version)) {
             return null;

compat/maven-embedder/src/main/java/org/apache/maven/cli/ResolveFile.java

@@ -21,11 +21,15 @@
 import java.io.File;
 import java.nio.file.Paths;
 
+import org.apache.maven.api.annotations.Nullable;
+
 /**
  * Resolve relative file path against the given base directory
  */
 @Deprecated
 public class ResolveFile {
+
+    @Nullable
     public static File resolveFile(File file, String baseDirectory) {
         if (file == null) {
             return null;

compat/maven-embedder/src/main/java/org/apache/maven/cli/logging/Slf4jStdoutLogger.java

@@ -20,6 +20,7 @@
 
 import java.io.PrintStream;
 
+import org.apache.maven.api.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.Marker;
 
@@ -61,6 +62,7 @@ public void error(String msg, Throwable t) {
     //
     // Don't need any of this
     //
+    @Nullable
     public String getName() {
         return null;
     }

compat/maven-embedder/src/main/java/org/apache/maven/cli/props/MavenProperties.java

@@ -44,6 +44,7 @@
 import java.util.Set;
 import java.util.function.UnaryOperator;
 
+import org.apache.maven.api.annotations.Nullable;
 import org.apache.maven.impl.model.DefaultInterpolator;
 
 /**
@@ -272,6 +273,7 @@ void putAllSubstituted(Map<? extends String, ? extends String> m) {
         storage.putAll(m);
     }
 
+    @Nullable
     public String put(String key, List<String> commentLines, List<String> valueLines) {
         commentLines = new ArrayList<>(commentLines);
         valueLines = new ArrayList<>(valueLines);
@@ -305,6 +307,7 @@ public String put(String key, List<String> commentLines, List<String> valueLines
         return storage.put(key, property[1]);
     }
 
+    @Nullable
     public String put(String key, List<String> commentLines, String value) {
         commentLines = new ArrayList<>(commentLines);
         this.layout.put(key, new Layout(commentLines, null));
@@ -843,6 +846,7 @@ public PropertiesReader(Reader reader, boolean maybeTyped) {
          *
          * @throws IOException in case of an I/O error
          */
+        @Nullable
         public String readProperty() throws IOException {
             commentLines.clear();
             valueLines.clear();

compat/maven-model-builder/src/main/java/org/apache/maven/model/building/DefaultModelBuildingResult.java

@@ -24,6 +24,7 @@
 import java.util.Map;
 import java.util.Objects;
 
+import org.apache.maven.api.annotations.Nullable;
 import org.apache.maven.model.Model;
 import org.apache.maven.model.Profile;
 
@@ -81,11 +82,13 @@ public DefaultModelBuildingResult addModelId(String modelId) {
     }
 
     @Override
+    @Nullable
     public Model getRawModel() {
         return rawModels.get(modelIds.get(0));
     }
 
     @Override
+    @Nullable
     public Model getRawModel(String modelId) {
         return rawModels.get(modelId);
     }
@@ -100,6 +103,7 @@ public DefaultModelBuildingResult setRawModel(String modelId, Model rawModel) {
     }
 
     @Override
+    @Nullable
     public List<Profile> getActivePomProfiles(String modelId) {
         return activePomProfiles.get(modelId);
     }

compat/maven-model-builder/src/main/java/org/apache/maven/model/building/FileModelSource.java

@@ -23,6 +23,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 
+import org.apache.maven.api.annotations.Nullable;
 import org.apache.maven.building.FileSource;
 
 /**
@@ -58,6 +59,7 @@ public File getPomFile() {
     }
 
     @Override
+    @Nullable
     public ModelSource2 getRelatedSource(String relPath) {
         relPath = relPath.replace('\\', File.separatorChar).replace('/', File.separatorChar);