[SOLR-3160] Division by zero in StatsComponent with date field always missing

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.5
• Fix Version/s: 3.6, 4.0-ALPHA
• Assignee: Erick Erickson
• Reporter: Luca Cavanna
• Created: 24/Feb/12 09:55
• Updated: 10/May/13 10:38
• Resolved: 24/Feb/12 14:39

Description

Using the StatsComponent with a date field that never has a value you'll get

java.lang.ArithmeticException: / by zero at org.apache.solr.handler.component.DateStatsValues.addTypeSpecificStats (StatsValuesFactory.java:384)

The problem is in this line of DateStatsValues:

res.add("mean", new Date(sum / count));

If count is 0 the division throws ArithmeticException because sum is long here. This doesn't happen with NumericStatsValues because sum is double there and the division result is Nan.
By the way, the result of those divisions is not even included in the output when count is 0 because of this condition in SimpleStats#getStatsFields:

if (isShard == true || (Long) stv.get("count") > 0) {
    res.add(f, stv);
} else {
    res.add(f, null);
}

Therefore, it should never throw an exception!