Always return boolean in has filter

[ianks]

Previously, filter_array could return nil in certain cases which breaks the expectation that has should return a boolean. This PR fixes that.

[Copilot]

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test/integration/standard_filter_test.rb:984

• [nitpick] The duplicate assertion in test_has_with_boolean_input may be redundant; consider removing one to avoid unnecessary repetition in the test suite.

assert_template_result("Result: false", template, { "a0" => false })