Update divideSeries handling of missing denominators

[carrieedwards]

This PR updates the divideSeries function's handling of the case in which the denominator(s) are missing. Previously, CarbonAPI would return an error if the length of denominators was equal to zero. This appears to be inconsistent with how Graphite web handles this scenario, in which a value of None was returned for each value in the returned series (see here). In this case, instead of None, math.NaN() is returned. This is consistent with how asPercent handles missing values.

[npazosmendez]

LGTM

[grafanabot]

Go coverage report:

Click to expand.

File	%
github.com/grafana/carbonapi/cmd/carbonapi/http/capability.go	0.0%
github.com/grafana/carbonapi/cmd/carbonapi/http/enrichcontext.go	6.7%
github.com/grafana/carbonapi/cmd/carbonapi/http/find_handlers.go	33.5%
github.com/grafana/carbonapi/cmd/carbonapi/http/functions_handler.go	0.0%
github.com/grafana/carbonapi/cmd/carbonapi/http/helper.go	27.3%
github.com/grafana/carbonapi/cmd/carbonapi/http/info_handlers.go	53.8%
github.com/grafana/carbonapi/cmd/carbonapi/http/init.go	84.6%
github.com/grafana/carbonapi/cmd/carbonapi/http/lbcheck_handler.go	0.0%
github.com/grafana/carbonapi/cmd/carbonapi/http/metrics.go	0.0%
github.com/grafana/carbonapi/cmd/carbonapi/http/render_handler.go	50.0%
github.com/grafana/carbonapi/cmd/carbonapi/http/tags_handler.go	0.0%
github.com/grafana/carbonapi/cmd/carbonapi/http/usage_handler.go	0.0%
github.com/grafana/carbonapi/cmd/carbonapi/http/version_handler.go	0.0%
github.com/grafana/carbonapi/date/date.go	78.9%
github.com/grafana/carbonapi/expr/consolidations/consolidations.go	44.5%
github.com/grafana/carbonapi/expr/expr.go	31.0%
github.com/grafana/carbonapi/expr/functions/absolute/function.go	80.0%
github.com/grafana/carbonapi/expr/functions/aggregate/function.go	82.2%
github.com/grafana/carbonapi/expr/functions/aggregateLine/function.go	81.0%
github.com/grafana/carbonapi/expr/functions/aggregateSeriesLists/function.go	73.5%
github.com/grafana/carbonapi/expr/functions/aggregateWithWildcards/function.go	86.7%
github.com/grafana/carbonapi/expr/functions/alias/function.go	83.3%
github.com/grafana/carbonapi/expr/functions/aliasByBase64/function.go	88.6%
github.com/grafana/carbonapi/expr/functions/aliasByMetric/function.go	92.9%
github.com/grafana/carbonapi/expr/functions/aliasByNode/function.go	84.2%
github.com/grafana/carbonapi/expr/functions/aliasByRedis/function.go	72.1%
github.com/grafana/carbonapi/expr/functions/aliasSub/function.go	80.0%
github.com/grafana/carbonapi/expr/functions/asPercent/function.go	77.6%
github.com/grafana/carbonapi/expr/functions/averageOutsidePercentile/function.go	89.3%
github.com/grafana/carbonapi/expr/functions/averageSeriesWithWildcards/function.go	89.4%
github.com/grafana/carbonapi/expr/functions/below/function.go	91.7%
github.com/grafana/carbonapi/expr/functions/cactiStyle/function.go	88.7%
github.com/grafana/carbonapi/expr/functions/changed/function.go	92.3%
github.com/grafana/carbonapi/expr/functions/constantLine/function.go	88.2%
github.com/grafana/carbonapi/expr/functions/delay/function.go	90.6%
github.com/grafana/carbonapi/expr/functions/derivative/function.go	93.8%
github.com/grafana/carbonapi/expr/functions/divideSeries/function.go	87.7%
github.com/grafana/carbonapi/expr/functions/ewma/function.go	90.0%
github.com/grafana/carbonapi/expr/functions/exclude/function.go	81.8%
github.com/grafana/carbonapi/expr/functions/exp/function.go	90.9%
github.com/grafana/carbonapi/expr/functions/exponentialMovingAverage/function.go	72.2%
github.com/grafana/carbonapi/expr/functions/fallbackSeries/function.go	86.7%
github.com/grafana/carbonapi/expr/functions/filter/function.go	84.4%
github.com/grafana/carbonapi/expr/functions/grep/function.go	81.8%
github.com/grafana/carbonapi/expr/functions/groupByNode/function.go	86.5%
github.com/grafana/carbonapi/expr/functions/groupByTags/function.go	90.0%
github.com/grafana/carbonapi/expr/functions/heatMap/function.go	86.4%
github.com/grafana/carbonapi/expr/functions/heatMap/helpers.go	84.6%
github.com/grafana/carbonapi/expr/functions/highestLowest/function.go	87.1%
github.com/grafana/carbonapi/expr/functions/hitcount/function.go	93.8%
github.com/grafana/carbonapi/expr/functions/identity/function.go	89.5%
github.com/grafana/carbonapi/expr/functions/integral/function.go	94.4%
github.com/grafana/carbonapi/expr/functions/integralByInterval/function.go	85.4%
github.com/grafana/carbonapi/expr/functions/integralWithReset/function.go	86.1%
github.com/grafana/carbonapi/expr/functions/interpolate/function.go	92.1%
github.com/grafana/carbonapi/expr/functions/invert/function.go	93.3%
github.com/grafana/carbonapi/expr/functions/isNotNull/function.go	93.8%
github.com/grafana/carbonapi/expr/functions/join/function.go	89.5%
github.com/grafana/carbonapi/expr/functions/keepLastValue/function.go	92.5%
github.com/grafana/carbonapi/expr/functions/legendValue/function.go	90.9%
github.com/grafana/carbonapi/expr/functions/limit/function.go	82.4%
github.com/grafana/carbonapi/expr/functions/linearRegression/function.go	80.0%
github.com/grafana/carbonapi/expr/functions/logarithm/function.go	90.9%
github.com/grafana/carbonapi/expr/functions/logit/function.go	91.3%
github.com/grafana/carbonapi/expr/functions/lowPass/function.go	89.3%
github.com/grafana/carbonapi/expr/functions/mapSeries/function.go	88.0%
github.com/grafana/carbonapi/expr/functions/minMax/function.go	86.7%
github.com/grafana/carbonapi/expr/functions/mostDeviant/function.go	88.6%
github.com/grafana/carbonapi/expr/functions/moving/function.go	82.3%
github.com/grafana/carbonapi/expr/functions/movingMedian/function.go	86.3%
github.com/grafana/carbonapi/expr/functions/multiplySeriesWithWildcards/function.go	90.2%
github.com/grafana/carbonapi/expr/functions/nPercentile/function.go	90.0%
github.com/grafana/carbonapi/expr/functions/nonNegativeDerivative/function.go	90.5%
github.com/grafana/carbonapi/expr/functions/offset/function.go	88.0%
github.com/grafana/carbonapi/expr/functions/offsetToZero/function.go	94.1%
github.com/grafana/carbonapi/expr/functions/pearson/function.go	86.1%
github.com/grafana/carbonapi/expr/functions/pearsonClosest/function.go	75.0%
github.com/grafana/carbonapi/expr/functions/perSecond/function.go	90.5%
github.com/grafana/carbonapi/expr/functions/percentileOfSeries/function.go	81.8%
github.com/grafana/carbonapi/expr/functions/polyfit/function.go	87.3%
github.com/grafana/carbonapi/expr/functions/pow/function.go	88.9%
github.com/grafana/carbonapi/expr/functions/powSeries/function.go	95.0%
github.com/grafana/carbonapi/expr/functions/rangeOfSeries/function.go	94.3%
github.com/grafana/carbonapi/expr/functions/removeBelowSeries/function.go	92.3%
github.com/grafana/carbonapi/expr/functions/removeBetweenPercentile/function.go	89.2%
github.com/grafana/carbonapi/expr/functions/removeEmptySeries/function.go	90.0%
github.com/grafana/carbonapi/expr/functions/round/function.go	90.0%
github.com/grafana/carbonapi/expr/functions/scale/function.go	88.6%
github.com/grafana/carbonapi/expr/functions/scaleToSeconds/function.go	88.5%
github.com/grafana/carbonapi/expr/functions/seriesList/function.go	65.2%
github.com/grafana/carbonapi/expr/functions/sigmoid/function.go	91.3%
github.com/grafana/carbonapi/expr/functions/sinFunction/function.go	86.2%
github.com/grafana/carbonapi/expr/functions/slo/function.go	84.0%
github.com/grafana/carbonapi/expr/functions/slo/helpers.go	72.0%
github.com/grafana/carbonapi/expr/functions/smartSummarize/function.go	90.8%
github.com/grafana/carbonapi/expr/functions/sortBy/function.go	85.7%
github.com/grafana/carbonapi/expr/functions/sortByName/function.go	85.2%
github.com/grafana/carbonapi/expr/functions/squareRoot/function.go	90.5%
github.com/grafana/carbonapi/expr/functions/substr/function.go	85.4%
github.com/grafana/carbonapi/expr/functions/sumSeriesWithWildcards/function.go	89.1%
github.com/grafana/carbonapi/expr/functions/summarize/function.go	91.7%
github.com/grafana/carbonapi/expr/functions/timeShift/function.go	78.0%
github.com/grafana/carbonapi/expr/functions/timeShiftByMetric/function.go	89.7%
github.com/grafana/carbonapi/expr/functions/timeShiftByMetric/misc.go	93.8%
github.com/grafana/carbonapi/expr/functions/transformNull/function.go	88.7%
github.com/grafana/carbonapi/expr/functions/tukey/function.go	80.8%
github.com/grafana/carbonapi/expr/functions/unique/function.go	88.9%
github.com/grafana/carbonapi/expr/functions/weightedAverage/function.go	85.7%
github.com/grafana/carbonapi/expr/helper/align.go	60.7%
github.com/grafana/carbonapi/expr/helper/helper.go	0.0%
github.com/grafana/carbonapi/expr/helper/metric/extract.go	72.7%
github.com/grafana/carbonapi/expr/helper/sort.go	0.0%
github.com/grafana/carbonapi/expr/rewrite/aboveSeries/function.go	79.3%
github.com/grafana/carbonapi/expr/sort.go	96.1%
github.com/grafana/carbonapi/expr/tags/helper.go	100.0%
github.com/grafana/carbonapi/expr/types/extract.go	82.4%
github.com/grafana/carbonapi/expr/types/list.go	0.0%
github.com/grafana/carbonapi/expr/types/metricheap.go	0.0%
github.com/grafana/carbonapi/expr/types/types.go	33.9%
github.com/grafana/carbonapi/expr/types/windowed.go	0.0%
github.com/grafana/carbonapi/pkg/parser/define.go	76.9%
github.com/grafana/carbonapi/pkg/parser/interface.go	0.0%
github.com/grafana/carbonapi/pkg/parser/internal.go	9.4%
github.com/grafana/carbonapi/pkg/parser/interval.go	83.8%
github.com/grafana/carbonapi/pkg/parser/parser.go	44.3%
github.com/grafana/carbonapi/zipper/broadcast/broadcast_group.go	38.5%
github.com/grafana/carbonapi/zipper/helper/requests.go	13.3%
github.com/grafana/carbonapi/zipper/protocols/graphite/msgpack/type_gen.go	57.2%
github.com/grafana/carbonapi/zipper/protocols/irondb/irondb_group.go	2.5%
github.com/grafana/carbonapi/zipper/protocols/irondb/irondb_helpers.go	81.1%
github.com/grafana/carbonapi/zipper/protocols/prometheus/helpers/helpers.go	17.1%
github.com/grafana/carbonapi/zipper/protocols/victoriametrics/feature_set.go	19.7%
github.com/grafana/carbonapi/zipper/protocols/victoriametrics/fetch.go	0.0%
github.com/grafana/carbonapi/zipper/protocols/victoriametrics/find.go	0.0%
github.com/grafana/carbonapi/zipper/protocols/victoriametrics/tags.go	0.0%
github.com/grafana/carbonapi/zipper/protocols/victoriametrics/victoriametrics_group.go	7.8%
github.com/grafana/carbonapi/zipper/types/backend.go	0.0%
github.com/grafana/carbonapi/zipper/types/errors.go	0.0%
github.com/grafana/carbonapi/zipper/types/lbmethod.go	0.0%
github.com/grafana/carbonapi/zipper/types/requests.go	0.0%
github.com/grafana/carbonapi/zipper/types/response.go	6.4%
github.com/grafana/carbonapi/zipper/types/stats.go	0.0%
github.com/grafana/carbonapi/zipper/zipper.go	0.0%
github.com/grafana/carbonapi/zipper/zipper_pb3.go	0.0%
total	55.5%

Go lint report:

No issues found. 😎