Do not set flag_value as None in click Option

From click 8.3.0 flag_value is set as a sentinel
value UNSET instead of None, and since we maintain
a PluggableCommanLineOption subclass, we need to
maintain the same default values for an Option to
avoid issues.

Reference: https://github.com/pallets/click/releases/tag/8.3.0
Reference: aboutcode-org/scancode-toolkit#4572
Signed-off-by: Ayan Sinha Mahapatra <[email protected]>

Author: AyanSinhaMahapatra

src/commoncode/cliutils.py

@@ -22,6 +22,19 @@
 # Tracing flags
 TRACE = False
 
+try:
+    # Introduced in click 8.3.0 to have a sentinel value
+    # (https://peps.python.org/pep-0661/) for flag values
+    # and default values instead of None to differentiate
+    # between explicitly setting a `None` value and
+    # not setting and value.
+    # See https://github.com/pallets/click/pull/3030 and
+    # https://github.com/pallets/click/releases/tag/8.3.0
+    from click.core import UNSET
+except ImportError:
+    # to maintain compatibility with click < 8.3.0
+    UNSET = None
+
 
 def logger_debug(*args):
     pass
@@ -429,7 +442,7 @@ def __init__(
         confirmation_prompt=False,
         hide_input=False,
         is_flag=None,
-        flag_value=None,
+        flag_value=UNSET,
         multiple=False,
         count=False,
         allow_from_autoenv=True,