Improve error handling by validating inputs and outputs of functions

[tkilias]

Background

• We got at some point the following error message

  [Code: 0, SQL State: 43000] "attempt to index a nil value (field 'integer index')" caught in script "IDA"."SME_DEPLOY_SAGEMAKER_AUTOPILOT_ENDPOINT" at line 402 (Session: 1775016774761775104)

• This error is caused by something which is nil, but shouldn't be nil, we should check this before we're accessing and throw proper error messages.

• It is likely, that the following line caused the error

  sagemaker-extension/exasol_sagemaker_extension/resources/lua/outputs/create_statement_autopilot_endpoint_deployment_lua_script.sql

  Line 403 in 3b93869

  local target_column = metadata_row[1][1]

  • and that the metadata_row nil was, because the db_metadata_reader didn't find the metadata row for this particular job.
  • To get better error message, we should have checked in the db_metadata_reader, if the row was nil or not