Return a 404 on ResourceNotFoundException

Current implementation returns a 500, which is incorrect.
A ResourceNotFoundException indicates a resource could not
be found, which is REST translates to a 404 http code.

Returning a 404 will ensure that clients will be able
to correctly identify missing projects.

Bug: Issue 16730
Change-Id: Ifb331dcee7165b7b2f2b33879c6c3cd2edfe8cc2

src/main/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilter.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilter.java b/src/main/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilter.java
index 7027239..df43519 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilter.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilter.java
@@ -22,6 +22,7 @@
 import static javax.servlet.http.HttpServletResponse.SC_CREATED;
 import static javax.servlet.http.HttpServletResponse.SC_FORBIDDEN;
 import static javax.servlet.http.HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
+import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 import static javax.servlet.http.HttpServletResponse.SC_OK;
 
 import com.google.common.flogger.FluentLogger;
@@ -152,9 +153,12 @@
     } catch (ResourceConflictException e) {
       RestApiServlet.replyError(
           httpRequest, httpResponse, SC_CONFLICT, e.getMessage(), e.caching(), e);
-    } catch (InitProjectException | ResourceNotFoundException e) {
+    } catch (InitProjectException e) {
       RestApiServlet.replyError(
           httpRequest, httpResponse, SC_INTERNAL_SERVER_ERROR, e.getMessage(), e.caching(), e);
+    } catch (ResourceNotFoundException e) {
+      RestApiServlet.replyError(
+          httpRequest, httpResponse, SC_NOT_FOUND, e.getMessage(), e.caching(), e);
     } catch (NoSuchElementException e) {
       RestApiServlet.replyError(
           httpRequest, httpResponse, SC_BAD_REQUEST, "Project name not present in the url", e);

src/test/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilterTest.java

diff --git a/src/test/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilterTest.java b/src/test/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilterTest.java
index 2ed1466..bdad210 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilterTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/replication/pull/api/PullReplicationFilterTest.java
@@ -242,7 +242,7 @@
   }
 
   @Test
-  public void shouldBe500WhenResourceNotFound() throws Exception {
+  public void shouldBe404WhenResourceNotFound() throws Exception {
     when(request.getRequestURI()).thenReturn(DELETE_PROJECT_URI);
     when(request.getMethod()).thenReturn("DELETE");
     when(projectsCollection.parse(TopLevelResource.INSTANCE, IdString.fromDecoded(PROJECT_NAME)))
@@ -254,7 +254,7 @@
     final PullReplicationFilter pullReplicationFilter = createPullReplicationFilter();
     pullReplicationFilter.doFilter(request, response, filterChain);
 
-    verify(response).setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
+    verify(response).setStatus(HttpServletResponse.SC_NOT_FOUND);
   }
 
   @Test