Refactor duplicated TTL computation in DefaultRedisCacheWriter's get method

[diydriller]

Problem

In DefaultRedisCacheWriter's get method, following expression is evaluated twice

  timeToIdleEnabled && withTtl ? ttl : null

Proposed Improvement

Extract the conditional TTL evaluation into a single variable

  Duration ttlForGet = (timeToIdleEnabled && withTtl ? ttl : null);