list_datasets_per_rse error with filters dictionary
Motivation
----------
`[Wed Aug 28 13:22:08.394401 2019] [:error] [pid 5693:tid 139990440838912] Traceback (most recent call last):
[Wed Aug 28 13:22:08.394428 2019] [:error] [pid 5693:tid 139990440838912]   File "/usr/lib/python2.7/site-packages/rucio/web/rest/replica.py", line 826, in GET
[Wed Aug 28 13:22:08.394432 2019] [:error] [pid 5693:tid 139990440838912]     for row in list_datasets_per_rse(rse=rse):
[Wed Aug 28 13:22:08.394435 2019] [:error] [pid 5693:tid 139990440838912]   File "/usr/lib/python2.7/site-packages/rucio/api/replica.py", line 323, in list_datasets_per_rse
[Wed Aug 28 13:22:08.394437 2019] [:error] [pid 5693:tid 139990440838912]     if 'scope' in filters:
[Wed Aug 28 13:22:08.394440 2019] [:error] [pid 5693:tid 139990440838912] TypeError: argument of type 'NoneType' is not iterable`

Modification
------------
Change `filter = {}`
diff --git a/lib/rucio/api/replica.py b/lib/rucio/api/replica.py
index f5661af2f..eb7c2e372 100644
--- a/lib/rucio/api/replica.py
+++ b/lib/rucio/api/replica.py
@@ -19,6 +19,7 @@
 # - Mario Lassnig <mario.lassnig@cern.ch>, 2017-2019
 # - Hannes Hansen <hannes.jakob.hansen@cern.ch>, 2019
 # - Andrew Lister <andrew.lister@stfc.ac.uk>, 2019
+# - Martin Barisits <martin.barisits@cern.ch>, 2019
 #
 # PY3K COMPATIBLE
 
@@ -308,7 +309,7 @@ def list_dataset_replicas_vp(scope, name, deep=False):
         yield api_update_return_dict(r)
 
 
-def list_datasets_per_rse(rse, filters=None, limit=None):
+def list_datasets_per_rse(rse, filters={}, limit=None):
     """
     :param scope: The scope of the dataset.
     :param name: The name of the dataset.
diff --git a/lib/rucio/core/message.py b/lib/rucio/core/message.py
index 4a61e462b..b6c510e5c 100644
--- a/lib/rucio/core/message.py
+++ b/lib/rucio/core/message.py
@@ -15,7 +15,7 @@
 # Authors:
 # - Mario Lassnig <mario.lassnig@cern.ch>, 2014-2019
 # - Vincent Garonne <vgaronne@gmail.com>, 2014-2017
-# - Martin Barisits <martin.barisits@cern.ch>, 2014-2016
+# - Martin Barisits <martin.barisits@cern.ch>, 2014-2019
 # - Robert Illingworth <illingwo@fnal.gov>, 2018
 # - Hannes Hansen <hannes.jakob.hansen@cern.ch>, 2018
 #
@@ -29,6 +29,7 @@ from sqlalchemy.sql.expression import bindparam, text
 
 
 from rucio.common.exception import InvalidObject, RucioException
+from rucio.common.utils import APIEncoder
 from rucio.db.sqla.models import Message, MessageHistory
 from rucio.db.sqla.session import transactional_session
 
@@ -46,7 +47,7 @@ def add_message(event_type, payload, session=None):
     """
 
     try:
-        payload = json.dumps(payload)
+        payload = json.dumps(payload, cls=APIEncoder)
     except TypeError as e:
         raise InvalidObject('Invalid JSON for payload: %(e)s' % locals())
 
diff --git a/lib/rucio/daemons/conveyor/finisher.py b/lib/rucio/daemons/conveyor/finisher.py
index f3b303c32..2874ae232 100644
--- a/lib/rucio/daemons/conveyor/finisher.py
+++ b/lib/rucio/daemons/conveyor/finisher.py
@@ -16,7 +16,7 @@
 # - Wen Guan <wguan.icedew@gmail.com>, 2015-2016
 # - Mario Lassnig <mario.lassnig@cern.ch>, 2015
 # - Vincent Garonne <vgaronne@gmail.com>, 2015-2018
-# - Martin Barisits <martin.barisits@cern.ch>, 2015-2017
+# - Martin Barisits <martin.barisits@cern.ch>, 2015-2019
 # - Cedric Serfon <cedric.serfon@cern.ch>, 2017-2018
 # - Hannes Hansen <hannes.jakob.hansen@cern.ch>, 2018
 # - Andrew Lister <andrew.lister@stfc.ac.uk>, 2019
@@ -251,8 +251,8 @@ def __handle_requests(reqs, suspicious_patterns, retry_protocol_mismatches, prep
                 __check_suspicious_files(req, suspicious_patterns)
                 tss = time.time()
                 try:
-                    new_req = request_core.requeue_and_archive(req, retry_protocol_mismatches)
-                    if new_req:
+                    if request_core.should_retry_request(req, retry_protocol_mismatches):
+                        new_req = request_core.requeue_and_archive(req, retry_protocol_mismatches)
                         # should_retry_request and requeue_and_archive are not in one session,
                         # another process can requeue_and_archive and this one will return None.
                         record_timer('daemons.conveyor.common.update_request_state.request-requeue_and_archive', (time.time() - tss) * 1000)
@@ -278,8 +278,8 @@ def __handle_requests(reqs, suspicious_patterns, retry_protocol_mismatches, prep
                     continue
                 try:
                     tss = time.time()
-                    new_req = request_core.requeue_and_archive(req, retry_protocol_mismatches)
-                    if new_req:
+                    if request_core.should_retry_request(req, retry_protocol_mismatches):
+                        new_req = request_core.requeue_and_archive(req, retry_protocol_mismatches)
                         record_timer('daemons.conveyor.common.update_request_state.request-requeue_and_archive', (time.time() - tss) * 1000)
                         logging.warn(prepend_str + 'REQUEUED SUBMITTING DID %s:%s REQUEST %s AS %s TRY %s' % (req['scope'],
                                                                                                               req['name'],
['lib/rucio/api/replica.py', 'lib/rucio/daemons/conveyor/finisher.py', 'lib/rucio/core/message.py']