Improve default value handling for NULL value fields
Currently the default value handling for input fields that can be set to NULL (eval is set to null) is quite inconsistent when creating new records:
- if mode is set to useOrOverridePlaceholder the field is NULL by default
- if this setting is not used the default value is a non empty string
Additionally it is not possible to explicitly set a NULL default value.
It would be better to if the mode does not have any influence on the default value but if it is possible to set NULL as default.
When this is handled together with #53662 backward compatibility should not be a problem because currently new records will have NULL values by default but empty strings are stored in the database.
[TASK] Unify NULL default value handling
If a field is configured to allow NULL values ("eval" is set to "null")
and the default value in the TCA is explicitly set to NULL the value
will not be converted to a string.
Additionally the mode setting "useOrOverridePlaceholder" will not have
any influence any more on the default value when creating new records.
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Wouter Wolters
Reviewed-by: Oliver Hader
Reviewed-by: Ernesto Baschny
Reviewed-by: Stefan Neufeind
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe