Use is-None checks

Always test for None using identity comparisons (is None / is not None) rather than equality operators (==, !=) or implicit truthiness checks. Equality comparisons can behave unexpectedly with custom __eq__ implementations, and truthiness checks conflate None with other falsy values (empty string, 0, empty dict/list, False), which often have different meaning in the code. Identity checks are also faster since they avoid bool conversion.

Bad:

if domain != None:
    ...
if reqctx:  # loses distinction between None and a falsy-but-valid context
    ...
assert get_debug_flag() == None

Good:

if domain is not None:
    ...
if reqctx is not None:
    ...
assert get_debug_flag() is None

This is especially important when a value can legitimately be None, an empty string, or another falsy value, and these cases must be handled differently. For example, when merging configuration options where None should fall back to a default but an empty string or empty value should not:

url_prefix = options.get("url_prefix") or self.url_prefix
bp_url_prefix = bp_options.get("url_prefix") or blueprint.url_prefix
if bp_url_prefix and url_prefix:
    url_prefix = url_prefix.rstrip("/") + "/" + bp_url_prefix.lstrip("/")

Similarly, when a key may be None and needs a default substitution, check explicitly for None rather than relying on truthiness:

key = self.name if key is None else f"{self.name}.{key}"

Apply this pattern consistently whenever a value, parameter, or return type is Optional, to prevent subtle bugs where None is silently treated the same as other falsy values (or vice versa).</description> </invoke>