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Collection Membership operator can return unintuitive results if collection has mix of types #1240

@davidding

Description

@davidding

Since the CollectionMembershipOperator coerces the type of the item being tested to the first (or first non-null) element in the list, it can lead to unexpected/unintuitive results.

for (Object value : collection) {
if (value == null) {
if (o1 == null) {
return Boolean.TRUE;
}
} else {
try {
return collection.contains(converter.convert(o1, value.getClass()));
} catch (ELException e) {
return Boolean.FALSE;
}
}
}
}

{{ null in [null, 1, 2] }} {# true #}
{{ null in [1, null, 2] }} {# false - null converted to 0; no 0 in list #}
{{ null in [1, null, 2, 0] }} {# true - because of the 0 in the list, not the null #}
{{ null in [0, 1, 2] }} {# true #}

{{ 1 in ['1', 2 ] }} {# true - 1 converted to '1' #}
{{ 2 in ['1', 2 ] }} {# false - 2 is converted to '2', no '2' in list #}
{{ 1 in [false, 1] }} {# false - 1 converted to true #}
{{ 1 in [true, 0] }} {# true #}
{{ 1 in [null, 'abc', 1] }} {# false #}

{{ '' in [1, '', 2] }} {# false #}
{{ '' in [0, 1, 2] }} {# true #}

(The same applies to is containing, e.g. [false, 1] is containing 1 is false)

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