Chameleon can utilize the Python None object to represent an empty value variable of any type.

	By default, the Python None object is disabled in Chameleon VMD files. For details on how to enable the Python None object, see Disabling/Enabling the Python None Object.

Therefore, the following type-independent if condition may be used to handle empty values:

if value == None:
   # Value is empty.
else:
   # Value is not empty.

It is also possible to set the value variable to the Python None object so that Chameleon will flag the field/column as being empty:

value = None

In previous versions of Chameleon, there was no special handling of empty values, which meant that empty string values were represented by empty strings "", while empty integers, doubles, and date times were all represented by 0. If your existing Python code assumes that these values are used to represent empty, you can place code at the beginning of each script that sets the value variable.

For string values, use the following:

if value == None:
   value = ""

For integer, double and datetime values, use the following:

if value == None:
   value = 0