Error:
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Storing NULL values using the following code does not work.

$attribute->setAttribute( 'data_float3', null );
$ezpersistentobject->storeObject(...);

Because of the defintion in ezcontentclassattribute.php the null-values are being replaced in favor of the defined default_value, which is 0 (zero) for all numeric based datatypes.

Expected behaviour:
-------------------

$attribute->setAttribute( 'date_float3', null);
$ezpersistentobject->storeObject(...);

Should store the assigned value 'null' into database.

Sideeffects:
-----------------
eZFloat, eZInteger, ... (numeric based) datatypes is usable when the empty string is replaced with null. If a contentclass-attribute is marked 'not required', the database really stores null and not some faked 0 (zero) value which is NOT the value the user has typed in.

Steps to reproduce

Create a contentclass, use eZInteger or eZFloat or any other Datatype. This Datatype can be a core datatype or submitted by the community.

The used Datatype should not be required. Min/Max/Default must be left empty.

Create a contentobject using this class.
Do not type anything in.
Save.

Result:
--------
The value (data_int3, data_float3) have 0 (zero) as value which is obviously wrong by the database definition which can have NULL values.