default

The default filter returns the passed default value if the value is undefined or empty, otherwise the value of the variable:

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{{ var|default('var is not defined') }}

{{ var.foo|default('foo item on var is not defined') }}

{{ var['foo']|default('foo item on var is not defined') }}

{{ ''|default('passed var is empty')  }}

When using the default filter on an expression that uses variables in some method calls, be sure to use the default filter whenever a variable can be undefined:

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{{ var.method(foo|default('foo'))|default('foo') }}

Using the default filter on a boolean variable might trigger unexpected behavior, as false is treated as an empty value. Consider using ?? instead:

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{% set foo = false %}
{{ foo|default(true) }} {# true #}
{{ foo ?? true }} {# false #}