For normal host variables in an application program, when selecting a NULL value into a host variable, a negative value is assigned to the indicator variable signifying that the value is NULL. In the case of LOB locators, however, the meaning of indicator variables is slightly different.
Since a locator host variable itself can never be NULL, a negative indicator variable value indicates that the LOB value represented by the LOB locator is NULL. The NULL information is kept local to the client using the indicator variable value. The server does not track NULL values with valid locators.