fix(feed-fetch): fix NPEs encountered during feed fetch operations.

fixes #127

Author: landonreed

src/main/java/com/conveyal/datatools/manager/jobs/FetchProjectFeedsJob.java

@@ -30,6 +30,11 @@ public FetchProjectFeedsJob (Project project, String owner) {
     @Override
     public void jobLogic() {
         Project project = Persistence.projects.getById(projectId);
+        if (project == null) {
+            LOG.error("Fetch feeds job failed because project {} does not exist in database. Clearing the project's scheduled fetch jobs.");
+            DataManager.autoFetchMap.remove(projectId);
+            return;
+        }
         LOG.info("Fetch job running for {} project at {}", project.name, ZonedDateTime.now(ZoneId.of("America/New_York")));
         Collection<FeedSource> projectFeeds = project.retrieveProjectFeedSources();
         for(FeedSource feedSource : projectFeeds) {

src/main/java/com/conveyal/datatools/manager/jobs/FetchSingleFeedJob.java

@@ -34,12 +34,14 @@ public FetchSingleFeedJob (FeedSource feedSource, String owner, boolean continue
      */
     @JsonProperty
     public String getFeedVersionId () {
-        return result.id;
+        // Feed version result is null unless (and until) fetch is successful.
+        return result != null ? result.id : null;
     }
 
     @JsonProperty
     public String getFeedSourceId () {
-        return result.parentFeedSource().id;
+        // Feed version result is null unless (and until) fetch is successful.
+        return result != null ? result.parentFeedSource().id : null;
     }
 
     @Override

src/main/java/com/conveyal/datatools/manager/models/FeedSource.java

@@ -151,8 +151,6 @@ public FeedVersion fetch (MonitorableJob.Status status) {
     public FeedVersion fetch (MonitorableJob.Status status, String optionalUrlOverride) {
         status.message = "Downloading file";
 
-        FeedVersion latest = retrieveLatest();
-
         // We create a new FeedVersion now, so that the fetched date is (milliseconds) before
         // fetch occurs. That way, in the highly unlikely event that a feed is updated while we're
         // fetching it, we will not miss a new feed.
@@ -189,7 +187,8 @@ public FeedVersion fetch (MonitorableJob.Status status, String optionalUrlOverri
         }
 
         conn.setDefaultUseCaches(true);
-
+        // Get latest version to check that the fetched version does not duplicate a feed already loaded.
+        FeedVersion latest = retrieveLatest();
         // lastFetched is set to null when the URL changes and when latest feed version is deleted
         if (latest != null && this.lastFetched != null)
             conn.setIfModifiedSince(Math.min(latest.updated.getTime(), this.lastFetched.getTime()));