NULL value is returned instead of an expected empty string when using Oracle
Oracle currently treats a character value with a length of zero as null. If you store an empty string ("") in a nullable Oracle column, the data returned via the REST API or the dashboard will contain a null and not an empty string.
About this task
To resolve this problem, use a specific string instead of an empty string as a value for a metric to avoid this problem. For example, replace the empty string with '~' or 'None' in the metric default value, and write a metric map expression to remove empty strings if they are found in event data.