DynamoDB BETWEEN incorrectly excludes attribute value 0

Bug

DynamoDB BETWEEN filtering incorrectly excludes items whose attribute value is exactly 0, even when 0 is within the specified range.

Reproduction

An item with:

price = 0

is incorrectly excluded from:

price BETWEEN 0 AND 100

while an item with price = 5 is included.

Root cause

FuncBetween.expr() checks the tested attribute using bare Python truthiness (and attr). Since Decimal("0") is falsy, an attribute whose value is zero incorrectly fails the condition.

The start and end operands already use zero-safe checks for this exact reason, but attr does not.

Expected behavior

An attribute value of 0 should be included when it falls within the specified BETWEEN range.