diff --git a/lib/galaxy/jobs/__init__.py b/lib/galaxy/jobs/__init__.py
index 3f8e33321ac2..7809d94871de 100644
--- a/lib/galaxy/jobs/__init__.py
+++ b/lib/galaxy/jobs/__init__.py
@@ -328,7 +328,7 @@ def __init__(self, app: MinimalManagerApp):
         """Parse the job configuration XML."""
         self.app = app
         self.runner_plugins = []
-        self.dynamic_params = None
+        self.dynamic_params: Optional[Dict[str, Any]] = None
         self.handlers = {}
         self.handler_runner_plugins = {}
         self.default_handler_id = None
@@ -432,7 +432,7 @@ def _configure_from_dict(self, job_config_dict):
                 continue
             self.runner_plugins.append(runner_info)
         if "dynamic" in job_config_dict:
-            self.dynamic_params = job_config_dict.get("dynamic", None)
+            self.dynamic_params = job_config_dict["dynamic"]
 
         # Parse handlers
         handling_config_dict = job_config_dict.get("handling", {})
@@ -830,12 +830,12 @@ def get_destinations(self, id_or_tag) -> Iterable[JobDestination]:
         """
         return self.destinations.get(id_or_tag, [])
 
-    def get_job_runner_plugins(self, handler_id):
+    def get_job_runner_plugins(self, handler_id: str):
         """Load all configured job runner plugins
 
         :returns: list of job runner plugins
         """
-        rval = {}
+        rval: Dict[str, BaseJobRunner] = {}
         if handler_id in self.handler_runner_plugins:
             plugins_to_load = [rp for rp in self.runner_plugins if rp["id"] in self.handler_runner_plugins[handler_id]]
             log.info(
@@ -871,11 +871,9 @@ def get_job_runner_plugins(self, handler_id):
                     # If the name included a '.' or loading from the static runners path failed, try the original name
                     module = __import__(load)
                     module_name = load
-            if module is None:
-                # Module couldn't be loaded, error should have already been displayed
-                continue
             for comp in module_name.split(".")[1:]:
                 module = getattr(module, comp)
+            assert module  # make mypy happy
             if not class_names:
                 # If there's not a ':', we check <module>.__all__ for class names
                 try:
diff --git a/lib/galaxy/jobs/handler.py b/lib/galaxy/jobs/handler.py
index 2a455c8c425f..3cae6bf35750 100644
--- a/lib/galaxy/jobs/handler.py
+++ b/lib/galaxy/jobs/handler.py
@@ -231,7 +231,7 @@ class StopSignalException(Exception):
 class BaseJobHandlerQueue(Monitors):
     STOP_SIGNAL = object()
 
-    def __init__(self, app: MinimalManagerApp, dispatcher):
+    def __init__(self, app: MinimalManagerApp, dispatcher: "DefaultJobDispatcher"):
         """
         Initializes the Queue, creates (unstarted) monitoring thread.
         """
@@ -309,7 +309,8 @@ def __check_jobs_at_startup(self):
             with transaction(session):
                 session.commit()
 
-    def _check_job_at_startup(self, job):
+    def _check_job_at_startup(self, job: model.Job):
+        assert job.tool_id is not None
         if not self.app.toolbox.has_tool(job.tool_id, job.tool_version, exact=True):
             log.warning(f"({job.id}) Tool '{job.tool_id}' removed from tool config, unable to recover job")
             self.job_wrapper(job).fail(
@@ -1207,7 +1208,7 @@ def start(self):
         for runner in self.job_runners.values():
             runner.start()
 
-    def url_to_destination(self, url):
+    def url_to_destination(self, url: str):
         """This is used by the runner mapper (a.k.a. dynamic runner) and
         recovery methods to have runners convert URLs to destinations.
 
diff --git a/lib/galaxy/jobs/mapper.py b/lib/galaxy/jobs/mapper.py
index f5bac4e68407..66edbc10867e 100644
--- a/lib/galaxy/jobs/mapper.py
+++ b/lib/galaxy/jobs/mapper.py
@@ -2,6 +2,10 @@
 import logging
 from inspect import getfullargspec
 from types import ModuleType
+from typing import (
+    Callable,
+    TYPE_CHECKING,
+)
 
 import galaxy.jobs.rules
 from galaxy.jobs import stock_rules
@@ -9,6 +13,13 @@
 from galaxy.util.submodules import import_submodules
 from .rule_helper import RuleHelper
 
+if TYPE_CHECKING:
+    from galaxy.jobs import (
+        JobConfiguration,
+        JobDestination,
+        JobWrapper,
+    )
+
 log = logging.getLogger(__name__)
 
 DYNAMIC_RUNNER_NAME = "dynamic"
@@ -52,7 +63,12 @@ class JobRunnerMapper:
 
     rules_module: ModuleType
 
-    def __init__(self, job_wrapper, url_to_destination, job_config):
+    def __init__(
+        self,
+        job_wrapper: "JobWrapper",
+        url_to_destination: Callable[[str], "JobDestination"],
+        job_config: "JobConfiguration",
+    ):
         self.job_wrapper = job_wrapper
         self.url_to_destination = url_to_destination
         self.job_config = job_config
@@ -129,7 +145,7 @@ def __job_params(self, job):
         param_values = job.get_param_values(app, ignore_errors=True)
         return param_values
 
-    def __convert_url_to_destination(self, url):
+    def __convert_url_to_destination(self, url: str):
         """
         Job runner URLs are deprecated, but dynamic mapper functions may still
         be returning them.  Runners are expected to be able to convert these to
diff --git a/test/unit/app/jobs/test_mapper.py b/test/unit/app/jobs/test_mapper.py
index f2ec4cd1b87b..effd1fe71cd8 100644
--- a/test/unit/app/jobs/test_mapper.py
+++ b/test/unit/app/jobs/test_mapper.py
@@ -1,8 +1,11 @@
 import uuid
+from typing import cast
 
 from galaxy.jobs import (
     HasResourceParameters,
+    JobConfiguration,
     JobDestination,
+    JobWrapper,
 )
 from galaxy.jobs.mapper import (
     ERROR_MESSAGE_NO_RULE_FUNCTION,
@@ -134,10 +137,10 @@ def __assert_mapper_errors_with_message(mapper, message):
 
 
 def __mapper(tool_job_destination=TOOL_JOB_DESTINATION):
-    job_wrapper = MockJobWrapper(tool_job_destination)
-    job_config = MockJobConfig()
+    job_wrapper = cast(JobWrapper, MockJobWrapper(tool_job_destination))
+    job_config = cast(JobConfiguration, MockJobConfig())
 
-    mapper = JobRunnerMapper(job_wrapper, {}, job_config)
+    mapper = JobRunnerMapper(job_wrapper, lambda url: JobDestination(), job_config)
     mapper.rules_module = test_rules
     return mapper