An empty multimarker is AnyMarker, not EmptyMarker

src/poetry/core/version/markers.py

@@ -435,9 +435,12 @@ def of(cls, *markers: BaseMarker) -> BaseMarker:
 
                 new_markers.append(marker)
 
-        if any(m.is_empty() for m in new_markers) or not new_markers:
+        if any(m.is_empty() for m in new_markers):
             return EmptyMarker()
 
+        if not new_markers:
+            return AnyMarker()
+
         if len(new_markers) == 1:
             return new_markers[0]
 
@@ -577,6 +580,9 @@ def only(self, *marker_names: str) -> BaseMarker:
             if not marker.is_empty():
                 new_markers.append(marker)
 
+        if not new_markers:
+            return EmptyMarker()
+
         return self.of(*new_markers)
 
     def invert(self) -> BaseMarker:

tests/version/test_markers.py

@@ -373,6 +373,14 @@ def test_multi_complex_multi_marker_is_empty() -> None:
     assert m.is_empty()
 
 
+def test_multi_marker_is_any() -> None:
+    m1 = parse_marker('python_version != "3.6" or python_version == "3.6"')
+    m2 = parse_marker('python_version != "3.7" or python_version == "3.7"')
+
+    assert m1.intersect(m2).is_any()
+    assert m2.intersect(m1).is_any()
+
+
 def test_multi_marker_intersect_multi() -> None:
     m = parse_marker('sys_platform == "darwin" and implementation_name == "cpython"')
 
@@ -933,6 +941,7 @@ def test_without_extras(marker: str, expected: str) -> None:
     [
         ('python_version >= "3.6"', "implementation_name", 'python_version >= "3.6"'),
         ('python_version >= "3.6"', "python_version", "*"),
+        ('python_version >= "3.6" and python_version < "3.11"', "python_version", "*"),
         (
             'python_version >= "3.6" and extra == "foo"',
             "extra",