feat: add preset bool filter

project_manager/entry/detector.py

@@ -3,6 +3,18 @@ from pathlib import Path
 from .entry import Entry
 
 
+class EmptyEntry(Entry):
+    def __init__(self):
+        super().__init__({}, Path())
+
+    def __bool__(self):
+        return False
+
+
+ENTRY_NONE = EmptyEntry()
+ENTRY_SKIP = EmptyEntry()
+
+
 class EntryDetector:
-    def detect_entry(self, basepath: Path) -> Entry | None:
+    def detect_entry(self, basepath: Path) -> Entry:
         raise NotImplementedError