Throw an exception if a raw message has been deleted.

bramble-api/src/main/java/org/briarproject/bramble/api/client/ClientHelper.java

@@ -16,8 +16,6 @@ import org.briarproject.bramble.api.sync.MessageId;
 import java.security.GeneralSecurityException;
 import java.util.Map;
 
-import javax.annotation.Nullable;
-
 @NotNullByDefault
 public interface ClientHelper {
 
@@ -32,16 +30,12 @@ public interface ClientHelper {
 
 	Message createMessageForStoringMetadata(GroupId g);
 
-	@Nullable
 	Message getMessage(MessageId m) throws DbException;
 
-	@Nullable
 	Message getMessage(Transaction txn, MessageId m) throws DbException;
 
-	@Nullable
 	BdfList getMessageAsList(MessageId m) throws DbException, FormatException;
 
-	@Nullable
 	BdfList getMessageAsList(Transaction txn, MessageId m) throws DbException,
 			FormatException;
 

bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseComponent.java

@@ -298,12 +298,12 @@ public interface DatabaseComponent {
 			throws DbException;
 
 	/**
-	 * Returns the message with the given ID, in serialised form, or null if
-	 * the message has been deleted.
+	 * Returns the message with the given ID, in serialised form.
 	 * <p/>
 	 * Read-only.
+	 *
+	 * @throws MessageDeletedException if the message has been deleted
 	 */
-	@Nullable
 	byte[] getRawMessage(Transaction txn, MessageId m) throws DbException;
 
 	/**

bramble-api/src/main/java/org/briarproject/bramble/api/db/MessageDeletedException.java

@@ -0,0 +1,9 @@
+package org.briarproject.bramble.api.db;
+
+/**
+ * Thrown when a message that has been deleted is requested from the database.
+ * This exception may occur due to concurrent updates and does not indicate a
+ * database error.
+ */
+public class MessageDeletedException extends DbException {
+}