3 files changed, 29 insertions, 18 deletions

diff --git a/common/domain/mail.cpp b/common/domain/mail.cpp
index 6926711..3dd9093 100644
--- a/common/domain/mail.cpp
+++ b/common/domain/mail.cpp
@@ -59,8 +59,10 @@ void TypeImplementation<Mail>::configure(IndexPropertyMapper &indexPropertyMappe
     indexPropertyMapper.addIndexLookupProperty<Mail::ThreadId>([](TypeIndex &index, const ApplicationDomain::BufferAdaptor &entity) {
             auto messageId = entity.getProperty(Mail::MessageId::name);
             auto thread = index.secondaryLookup<Mail::MessageId, Mail::ThreadId>(messageId);
-            Q_ASSERT(!thread.isEmpty());
-            return thread.first();
+            if (!thread.isEmpty()) {
+                return thread.first();
+            }
+            return QByteArray{};  
         });
 }
 
diff --git a/common/mail/threadindexer.cpp b/common/mail/threadindexer.cpp
index 17ee31e..3da2fdd 100644
--- a/common/mail/threadindexer.cpp
+++ b/common/mail/threadindexer.cpp
@@ -84,9 +84,12 @@ void ThreadIndexer::updateThreadingIndex(const QByteArray &identifier, const App
 {
     auto messageId = entity.getProperty(Mail::MessageId::name);
     auto parentMessageId = entity.getProperty(Mail::ParentMessageId::name);
-    auto subject = entity.getProperty(Mail::Subject::name);
-
-    auto normalizedSubject = stripOffPrefixes(subject.toString()).toUtf8();
+    const auto subject = entity.getProperty(Mail::Subject::name);
+    const auto normalizedSubject = stripOffPrefixes(subject.toString()).toUtf8();
+    if (messageId.toByteArray().isEmpty()) {
+        SinkError() << "Found an email without messageId. This is illegal and threading will break. Entity id: " << identifier;
+        SinkError() << "Subject: " << subject;
+    }
 
     QVector<QByteArray> thread;
 
@@ -96,30 +99,29 @@ void ThreadIndexer::updateThreadingIndex(const QByteArray &identifier, const App
     //If parent is already available, add to thread of parent
     if (thread.isEmpty() && parentMessageId.isValid()) {
         thread = index().secondaryLookup<Mail::MessageId, Mail::ThreadId>(parentMessageId);
-        SinkTrace() << "Found parent";
+        SinkTrace() << "Found parent: " << thread;
     }
     if (thread.isEmpty()) {
         //Try to lookup the thread by subject:
         thread = index().secondaryLookup<Mail::Subject, Mail::ThreadId>(normalizedSubject);
         if (thread.isEmpty()) {
-            SinkTrace() << "Created a new thread ";
             thread << QUuid::createUuid().toByteArray();
+            SinkTrace() << "Created a new thread: " << thread;
         } else {
+            SinkTrace() << "Found thread by subject: " << thread;
         }
     }
 
-    //We should have found the thread by now
-    if (!thread.isEmpty()) {
-        if (parentMessageId.isValid()) {
-            //Register parent with thread for when it becomes available
-            index().index<Mail::MessageId, Mail::ThreadId>(parentMessageId, thread.first(), transaction);
-        }
-        index().index<Mail::MessageId, Mail::ThreadId>(messageId, thread.first(), transaction);
-        index().index<Mail::ThreadId, Mail::MessageId>(thread.first(), messageId, transaction);
-        index().index<Mail::Subject, Mail::ThreadId>(normalizedSubject, thread.first(), transaction);
-    } else {
-        SinkWarning() << "Couldn't find a thread for: " << messageId;
+    Q_ASSERT(!thread.isEmpty());
+
+    if (parentMessageId.isValid()) {
+        Q_ASSERT(!parentMessageId.toByteArray().isEmpty());
+        //Register parent with thread for when it becomes available
+        index().index<Mail::MessageId, Mail::ThreadId>(parentMessageId, thread.first(), transaction);
     }
+    index().index<Mail::MessageId, Mail::ThreadId>(messageId, thread.first(), transaction);
+    index().index<Mail::ThreadId, Mail::MessageId>(thread.first(), messageId, transaction);
+    index().index<Mail::Subject, Mail::ThreadId>(normalizedSubject, thread.first(), transaction);
 }
 
 
diff --git a/common/mailpreprocessor.cpp b/common/mailpreprocessor.cpp
index bde8a64..1366718 100644
--- a/common/mailpreprocessor.cpp
+++ b/common/mailpreprocessor.cpp
@@ -127,6 +127,13 @@ static void updatedIndexedProperties(Sink::ApplicationDomain::Mail &mail, KMime:
             parentMessageId = inReplyTo.first();
         }
     }
+    if (messageId.isEmpty()) {
+        auto tmp = KMime::Message::Ptr::create();
+        auto header = tmp->messageID(true);
+        header->generate("kube.kde.org");
+        messageId = header->as7BitString();
+        SinkWarning() << "Message id is empty, generating one: " << messageId;
+    }
 
     mail.setExtractedMessageId(messageId);
     if (!parentMessageId.isEmpty()) {