Steem Rocks - Internal Server Error When Click Potential Rewards for Steemit Users Who Did Not Write Posts in Last 7 Days

Steps:

1. Go http://steem.rocks
2. Enter Steemit Username who Who Did Not Write Posts in Last 7 Days such as "wang", "abit"
3. Click "Search"
4. Click "Potential Rewards" at Top Left
5. Observe

Expected Result: Page load without error for both Steemit users who wrote or not wrote any posts in last 7 days.

Actual Result: Internal Server Error When Click Potential Rewards for Authors Who Did Not Wrote Posts in Last 7 Days.

No Error Shown for Steemit Users who wrote posts in last 7 days.