Override FileBasedConfig's save method in MockConfig

This ensures we don't try to persist MockConfig using its superclasses
save() method which fails with an NPE since MockConfig has no backing
file.

Change-Id: Ifba2d24c9438bb30d3828ed31a4c131f940b45eb
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
diff --git a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java
index 8de386e..abbbf32 100644
--- a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java
+++ b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java
@@ -81,6 +81,11 @@ public void load() throws IOException, ConfigInvalidException {
 		}
 
 		@Override
+		public void save() throws IOException {
+			// Do nothing
+		}
+
+		@Override
 		public boolean isOutdated() {
 			return false;
 		}