From 6123ff144a76bc84b8f9a0b7303daf51a86e4b86 Mon Sep 17 00:00:00 2001
From: Gabriel Einsdorf <gabriel.einsdorf@uni-konstanz.de>
Date: Fri, 24 Aug 2018 13:06:54 +0200
Subject: [PATCH 1/2] DataHandleService: improve robustness of handle access

No longer throws NullPointerException when a handle can not be
created.
---
 .../java/org/scijava/io/handle/DataHandleService.java    | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/src/main/java/org/scijava/io/handle/DataHandleService.java b/src/main/java/org/scijava/io/handle/DataHandleService.java
index f2a24ba6d..0547e4cc8 100644
--- a/src/main/java/org/scijava/io/handle/DataHandleService.java
+++ b/src/main/java/org/scijava/io/handle/DataHandleService.java
@@ -33,7 +33,6 @@
 package org.scijava.io.handle;
 
 import java.io.IOException;
-import java.util.Objects;
 
 import org.scijava.io.IOService;
 import org.scijava.io.location.Location;
@@ -77,7 +76,7 @@ default Class<Location> getType() {
 	 */
 	default boolean exists(final Location location) throws IOException {
 		try (DataHandle<Location> handle = create(location)) {
-			return handle.exists();
+			return handle == null ? false : handle.exists();
 		}
 	}
 
@@ -89,8 +88,7 @@ default boolean exists(final Location location) throws IOException {
 	 * @see ReadBufferDataHandle#ReadBufferDataHandle(DataHandle)
 	 */
 	default DataHandle<Location> readBuffer(final DataHandle<Location> handle) {
-		Objects.nonNull(handle);
-		return new ReadBufferDataHandle(handle);
+		return handle == null ? null : new ReadBufferDataHandle(handle);
 	}
 
 	/**
@@ -113,7 +111,6 @@ default DataHandle<Location> readBuffer(final Location location) {
 	 * @see WriteBufferDataHandle#WriteBufferDataHandle(DataHandle)
 	 */
 	default DataHandle<Location> writeBuffer(final DataHandle<Location> handle) {
-		Objects.nonNull(handle);
-		return new WriteBufferDataHandle(handle);
+		return handle == null ? null : new WriteBufferDataHandle(handle);
 	}
 }

From db59c302cad50a6b937f97d65501ca4cbb255d25 Mon Sep 17 00:00:00 2001
From: Gabriel Einsdorf <gabriel.einsdorf@uni-konstanz.de>
Date: Fri, 14 Sep 2018 16:57:18 +0200
Subject: [PATCH 2/2] DataHandleService: document behavior when encountering
 null

---
 .../org/scijava/io/handle/DataHandleService.java   | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/main/java/org/scijava/io/handle/DataHandleService.java b/src/main/java/org/scijava/io/handle/DataHandleService.java
index 0547e4cc8..8bc55a2b6 100644
--- a/src/main/java/org/scijava/io/handle/DataHandleService.java
+++ b/src/main/java/org/scijava/io/handle/DataHandleService.java
@@ -71,8 +71,9 @@ default Class<Location> getType() {
 	 *
 	 * @param location the location to test
 	 * @return The result of {@link DataHandle#exists()} on a newly created handle
-	 *         on this location
-	 * @throws IOException
+	 *         on this location. Also returns {@code false} if the handle can not
+	 *         be created.
+	 * @throws IOException if the creation of the handle fails exceptionally
 	 */
 	default boolean exists(final Location location) throws IOException {
 		try (DataHandle<Location> handle = create(location)) {
@@ -85,6 +86,8 @@ default boolean exists(final Location location) throws IOException {
 	 * reading.
 	 *
 	 * @param handle the handle to wrap
+	 * @return The handle wrapped in a read-only buffer, or {@code null} if the
+	 *         input handle is {@code null}
 	 * @see ReadBufferDataHandle#ReadBufferDataHandle(DataHandle)
 	 */
 	default DataHandle<Location> readBuffer(final DataHandle<Location> handle) {
@@ -95,7 +98,10 @@ default DataHandle<Location> readBuffer(final DataHandle<Location> handle) {
 	 * Creates a {@link DataHandle} on the provided {@link Location} wrapped in a
 	 * read-only buffer for accelerated reading.
 	 *
-	 * @param location the handle to wrap
+	 * @param location the Location to create a buffered handle on.
+	 * @return A {@link DataHandle} on the provided location wrapped in a
+	 *         read-only buffer, or {@code null} if no handle could be created for
+	 *         the location.
 	 * @see ReadBufferDataHandle#ReadBufferDataHandle(DataHandle)
 	 */
 	default DataHandle<Location> readBuffer(final Location location) {
@@ -108,6 +114,8 @@ default DataHandle<Location> readBuffer(final Location location) {
 	 * accelerated writing.
 	 *
 	 * @param handle the handle to wrap
+	 * @return the handle wrapped in a write-only buffer or {@code null} if the
+	 *         provided handle is {@code null}
 	 * @see WriteBufferDataHandle#WriteBufferDataHandle(DataHandle)
 	 */
 	default DataHandle<Location> writeBuffer(final DataHandle<Location> handle) {