{% macro guarded_statement(property, source, statement) %}
{# If the property can be UNSET or None, this macro returns the provided statement guarded by an if which will check
 for those invalid values. Otherwise, it returns the statement unmodified. #}
{% if property.required and not property.nullable %}
{{ statement }}
{% else %}
    {% if property.nullable and not property.required %}
if not isinstance({{ source }}, Unset) and {{ source }} is not None:
    {{ statement }}
    {% elif property.nullable %}
if {{ source }} is not None:
    {{ statement }}
    {% else %}
if not isinstance({{ source }}, Unset):
    {{ statement }}
    {% endif %}
{% endif %}
{% endmacro %}