Null-annotated RefDatabase class

No other code changes except adding nullness annotations.

Change-Id: If2606fb208f6690bd4fd7ad953e709a3ebd6398c
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

org.eclipse.jgit/src/org/eclipse/jgit/lib/RefDatabase.java

@@ -51,6 +51,9 @@
 import java.util.List;
 import java.util.Map;
 
+import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.annotations.Nullable;
+
 /**
  * Abstraction of name to {@link ObjectId} mapping.
  * <p>
@@ -132,6 +135,7 @@ public abstract class RefDatabase {
 	 * @since 2.3
 	 * @see #isNameConflicting(String)
 	 */
+	@NonNull
 	public Collection<String> getConflictingNames(String name)
 			throws IOException {
 		Map<String, Ref> allRefs = getRefs(ALL);
@@ -169,6 +173,7 @@ public Collection<String> getConflictingNames(String name)
 	 * @throws IOException
 	 *             the reference space cannot be accessed.
 	 */
+	@NonNull
 	public abstract RefUpdate newUpdate(String name, boolean detach)
 			throws IOException;
 
@@ -183,6 +188,7 @@ public abstract RefUpdate newUpdate(String name, boolean detach)
 	 * @throws IOException
 	 *             the reference space cannot be accessed.
 	 */
+	@NonNull
 	public abstract RefRename newRename(String fromName, String toName)
 			throws IOException;
 
@@ -193,6 +199,7 @@ public abstract RefRename newRename(String fromName, String toName)
 	 *
 	 * @return a new batch update object.
 	 */
+	@NonNull
 	public BatchRefUpdate newBatchUpdate() {
 		return new BatchRefUpdate(this);
 	}
@@ -223,6 +230,7 @@ public boolean performsAtomicTransactions() {
 	 * @throws IOException
 	 *             the reference space cannot be accessed.
 	 */
+	@Nullable
 	public abstract Ref getRef(String name) throws IOException;
 
 	/**
@@ -238,6 +246,7 @@ public boolean performsAtomicTransactions() {
 	 *             the reference space cannot be accessed.
 	 * @since 4.1
 	 */
+	@Nullable
 	public Ref exactRef(String name) throws IOException {
 		Ref ref = getRef(name);
 		if (ref == null || !name.equals(ref.getName())) {
@@ -261,6 +270,7 @@ public Ref exactRef(String name) throws IOException {
 	 *             the reference space cannot be accessed.
 	 * @since 4.1
 	 */
+	@NonNull
 	public Map<String, Ref> exactRef(String... refs) throws IOException {
 		Map<String, Ref> result = new HashMap<>(refs.length);
 		for (String name : refs) {
@@ -285,6 +295,7 @@ public Map<String, Ref> exactRef(String... refs) throws IOException {
 	 *             the reference space cannot be accessed.
 	 * @since 4.1
 	 */
+	@Nullable
 	public Ref firstExactRef(String... refs) throws IOException {
 		for (String name : refs) {
 			Ref ref = exactRef(name);
@@ -308,6 +319,7 @@ public Ref firstExactRef(String... refs) throws IOException {
 	 * @throws IOException
 	 *             the reference space cannot be accessed.
 	 */
+	@NonNull
 	public abstract Map<String, Ref> getRefs(String prefix) throws IOException;
 
 	/**
@@ -322,6 +334,7 @@ public Ref firstExactRef(String... refs) throws IOException {
 	 * @throws IOException
 	 *             the reference space cannot be accessed.
 	 */
+	@NonNull
 	public abstract List<Ref> getAdditionalRefs() throws IOException;
 
 	/**
@@ -338,10 +351,11 @@ public Ref firstExactRef(String... refs) throws IOException {
 	 * @return {@code ref} if {@code ref.isPeeled()} is true; otherwise a new
 	 *         Ref object representing the same data as Ref, but isPeeled() will
 	 *         be true and getPeeledObjectId() will contain the peeled object
-	 *         (or null).
+	 *         (or {@code null}).
 	 * @throws IOException
 	 *             the reference space or object space cannot be accessed.
 	 */
+	@NonNull
 	public abstract Ref peel(Ref ref) throws IOException;
 
 	/**
@@ -365,9 +379,10 @@ public void refresh() {
 	 * @param name
 	 *            short name of ref to find, e.g. "master" to find
 	 *            "refs/heads/master" in map.
-	 * @return The first ref matching the name, or null if not found.
+	 * @return The first ref matching the name, or {@code null} if not found.
 	 * @since 3.4
 	 */
+	@Nullable
 	public static Ref findRef(Map<String, Ref> map, String name) {
 		for (String prefix : SEARCH_PATH) {
 			String fullname = prefix + name;