Allows add-on properties of type undefined to change type

[emmebi]

Allows for an add-on property which got an undefined DataType to be redefined with a different DataType.

Fixes #3819

Requirements for Contributing a Bug Fix or Enhancement

Identify the Bug or Feature request

Fixes #3819

Description of the Change

When we assign a property in an add-on with an empty string, the property gets the UNDEFINED data type; once this happens, it's not possible anymore for the property to change value.

This is because there is an explicit check which controls if we are storing in a property of one type a value which can be converted in that type. No value can be converted into the UNDEFINED value, hence the error.

This change relaxes the check so that the conversion logic is invoked only when there is no property with the same name or the property has UNDEFINED as the DataType of the value stored.

Possible Drawbacks

As this is a change in an existing behavior, it's possible that some add-on could break as a result of this. While I fail to see a reasonable use-case for this behavior, it doesn't mean that such an use-case doesn't exist.

Documentation Notes

Relevant lines

• https://github.com/RPTools/maptool/blob/develop/src/main/java/net/rptools/maptool/model/gamedata/MemoryDataStore.java#L193 - where we check if the data types of the new and old values are compatible
• https://github.com/RPTools/maptool/blob/develop/src/main/java/net/rptools/maptool/model/gamedata/data/DataType.java#L38 - no value can be converted to UNDEFINED
• https://github.com/RPTools/maptool/blob/develop/src/main/java/net/rptools/maptool/model/gamedata/MTScriptDataConversion.java#L80 - converting a string into a value; an empty string is here converted to an UNDEFINED data type

Release Notes

• Fixed add-on properties becoming unmutable after being assigned the empty string

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