Handle essql results with zero rows

[monfera]

Kibana version:
6., 7.

Describe the bug:
Based on this item:

filters
| essql ...
| pointseries ...
| plot ...
| render

will, in case of zero selected tuples, yield ⚠️ rather than, in increasing level of preference, one of

• a blank element
• a warning message
• a customizable error message
• alternative contents, eg. markup or image

[elasticmachine]

Pinging @elastic/kibana-canvas

[poffdeluxe]

Testing this in master, when an essql query has no results, essql returns a datatable with columns and no rows. That seems correct to me.

In addition, with #90481 being merged, instead of the math function throwing on the empty datatable, math has an onError function that can be set to null or zero if an exception (like empty datatable) is encountered in the expression.

The math function throwing an empty datatable exception seems like the biggest issue here now but now there's a way to address with with onError so I'm not sure what we'll want to do to make this easier for our users

[poffdeluxe]

@cqliu1 wrote this as a good workaround for situations where getCell might be throwing an exception due to no row:

filters
| essql query="SELECT * FROM \"kibana_sample_data_ecommerce\""
| shape "square" fill={
  switch case={case if={rowcount | eq 0} then="pink"} case={case if={getCell "failures" | compare "gte" "lte" to=20 to=50} then="#fca325"} case={case if={getCell "failures" | compare "gte" to=50} then="red"} case={case if={getCell "failures" | compare "lt" to=20} then="#2C6120"} case={case if={getCell "failures" | compare "eq" to=null} then="#2C6120"}
} border="rgba(255,255,255,0)" borderWidth=0 maintainAspect=false
| render

The rowcount as the first case will get evaluated first to avoid an error. Perhaps a solution to this whole problem would be to allow an onError flag for getCell like what the math function supports