fix comparer expected on is null

docs/info/release-history.rst

@@ -42,6 +42,7 @@ Changed
 Fixed
 -----
 * Paths are now sanitised when assigning ``filename`` to :py:class:`.LocalTrack`
+* :py:class:`.Comparer` no longer needs an expected value set for methods which do not use it
 
 
 1.2.0

musify/processors/compare.py

@@ -1,6 +1,7 @@
 """
 Processor making comparisons between objects and data types.
 """
+import inspect
 import re
 from collections.abc import Sequence, Hashable
 from datetime import datetime, date
@@ -89,7 +90,8 @@ def compare[T: Any](self, item: T, reference: T | None = None) -> bool:
 
         if reference is None and self.reference_required:
             raise ComparerError("A reference is required for this instance of Comparer")
-        if reference is None and not self.expected:
+        signature = inspect.getfullargspec(self._processor_method)
+        if reference is None and "expected" in signature.args and not self.expected:
             raise ComparerError("No comparative item given and no expected values set")
 
         tag_name = None

tests/processors/test_compare.py

@@ -67,6 +67,16 @@ def test_equality(self, obj: Comparer):
             new_filter.field = choice(obj.field.all())
         assert obj != new_filter
 
+    def test_compare_on_no_expected_value(self):
+        comparer = Comparer(condition="is null", field=LocalTrackField.DISC_TOTAL)
+        track = random_track()
+        track.disc_total = None
+
+        assert comparer.compare(track)
+
+        comparer = Comparer(condition="is not null", field=LocalTrackField.DISC_TOTAL)
+        assert not comparer.compare(track)
+
     def test_compare_with_reference(self):
         track_1 = random_track()
         track_2 = random_track()