Explicit None checks

Always distinguish “no value” (None) from other falsy values like 0, "", or False. Use is None / is not None for identity checks instead of truthy/falsy tests (if x or == None), since the latter can silently misbehave when a legitimate falsy value (e.g. port 0, an empty blueprint, etc.) is passed in. For example, prefer:

# Wrong: treats 0 as "no value"
port = int(port or sn_port or default_port)

# Right: only falls back when the value is actually None
port = int(next(p for p in (port, sn_port, default_port) if p is not None))

Likewise, keep existing is not None checks when refactoring code for style — do not simplify if x is not None: to if x: purely for brevity, as this changes behavior and can hide bugs.

When a variable may remain unset depending on a conditional/exception path, explicitly initialize it to None (or an appropriate default) before the branching logic, rather than relying on it being defined only inside a branch. For example, when capturing an exception for later use outside the handler, set error = None beforehand (or use an else clause) so the variable is never undefined, avoiding UnboundLocalError:

error = None
try:
    ...
except BuildError as e:
    error = e

Applying explicit is None checks and guaranteed initialization prevents subtle bugs around falsy-but-valid values and undefined variables, and makes intent clear to readers.</description>