I noticed something inconsistent with "null" value handling in ArcGIS Server.
While doing "Queries", null values are retrieved as null (see attachment). While doing Identifies, null values are retrieves as string : "Null" (see attachment)
These are examples of "Query" and "Identify" for the same data so you can notice the difference also illustrated in the attachment :
Query operation returns the value in the original data type.
Whereas Find and Identify operations return formatted string e.g. depending on the format assigned to the field, the return string may look like $123,345.90 or 9.054% etc.