Placeholder WarmUp compilation failures

Logs show that the placeholder WarmUp function occasionally fails to compile. This should never happen and hints at a specialization bug that should be fixed.

Kusto query (wus):

FunctionsLogs
| where PreciseTimeStamp > datetime(2018-06-11 16:00) and PreciseTimeStamp < datetime(2018-06-11 18:00)
| where Details contains "Exception while executing function: Functions.WarmUp"
| take 5

Start with the provided Kusto query for Functions.WarmUp compilation failures and inspect the logged exception details. Trace the placeholder WarmUp execution entry point and specialization path, then reproduce or isolate the intermittent failure. Done means the WarmUp function no longer fails to compile and the relevant failure scenario is covered by verification.

Written by the indexing model from the issue text.