Add support for an empty msg dict

Author: jteppinette

logfmter/formatter.py

@@ -126,7 +126,11 @@ def format(self, record: logging.LogRecord) -> str:
             extra = self.get_extra(record)
             params = {"msg": record.getMessage(), **extra}
 
-        tokens = ["at={}".format(record.levelname), self.format_params(params)]
+        tokens = ["at={}".format(record.levelname)]
+
+        formatted_params = self.format_params(params)
+        if formatted_params:
+            tokens.append(formatted_params)
 
         if record.exc_info:
             # Cast exc_info to its not null variant to make mypy happy.

tests/test_formatter.py

@@ -111,6 +111,9 @@ def test_get_extra(record, expected):
             },
             'at=INFO msg=alpha exc_info="Exception: alpha"',
         ),
+        # If, for some odd reason, someone passes in an empty msg dictionary. It
+        # should be properly formatted without extra spaces.
+        ({"levelname": "INFO", "msg": {}}, "at=INFO"),
     ],
 )
 def test_format(record, expected):