diff --git a/lib/galaxy/exceptions/__init__.py b/lib/galaxy/exceptions/__init__.py
index 88513f318a8e..d167a2e1fd00 100644
--- a/lib/galaxy/exceptions/__init__.py
+++ b/lib/galaxy/exceptions/__init__.py
@@ -30,7 +30,7 @@ class MessageException(Exception):
     # Error code information embedded into API json responses.
     err_code: ErrorCode = error_codes_by_name["UNKNOWN"]
 
-    def __init__(self, err_msg: str = "", type="info", **extra_error_info):
+    def __init__(self, err_msg: Optional[str] = None, type="info", **extra_error_info):
         self.err_msg = err_msg or self.err_code.default_error_message
         self.type = type
         self.extra_error_info = extra_error_info
@@ -64,7 +64,7 @@ class AcceptedRetryLater(MessageException):
     err_code = error_codes_by_name["ACCEPTED_RETRY_LATER"]
     retry_after: int
 
-    def __init__(self, msg: str, retry_after=60):
+    def __init__(self, msg: Optional[str] = None, retry_after=60):
         super().__init__(msg)
         self.retry_after = retry_after
 
@@ -136,7 +136,7 @@ class ToolMissingException(MessageException):
     status_code = 400
     err_code = error_codes_by_name["USER_TOOL_MISSING_PROBLEM"]
 
-    def __init__(self, err_msg: str = "", type="info", tool_id=None, **extra_error_info):
+    def __init__(self, err_msg: Optional[str] = None, type="info", tool_id=None, **extra_error_info):
         super().__init__(err_msg, type, **extra_error_info)
         self.tool_id = tool_id
 
@@ -152,7 +152,7 @@ class ToolInputsNotReadyException(MessageException):
 
 
 class ToolInputsNotOKException(MessageException):
-    def __init__(self, err_msg: str = "", type="info", *, src: str, id: int, **extra_error_info):
+    def __init__(self, err_msg: Optional[str] = None, type="info", *, src: str, id: int, **extra_error_info):
         super().__init__(err_msg, type, **extra_error_info)
         self.src = src
         self.id = id