You’ve probably already noticed this, but I should note for whoever else might be following along that both the label and the description of the “Null-safe access” checkbox are confusing. What it’s meant to address is data that missing from the input, not data that’s present but whose value is null – you don’t need to check this checkbox just to map a present-but-null value to the output.
The description (tool tip) for this setting is a bit more accurate:
Enable this to ignore missing data when accessing the source path, such as $a but a does not exist in the source data
The problem with that description is that “ignore” implies it will simply omit any value from the output. Instead, it maps it to a null value. What we’re looking for here is a way to actually do what this says – if a mapped value is missing from the input, don’t put anything in the output for it.
So, yes, there are a number of ways to approach a solution, depending on how flexible you want to get. A simple way would be to replace the “Null-safe access” checkbox with a 3-way choice:
Missing Data Policy:
- Error (equivalent to “Null-safe access” = false now)
- Map to null (equivalent to “Null-safe access” = true now)
- Omit (not possible now)
What I like about this approach is its simplicity. But it’s lacking some flexibility:
- One setting applies to all of the mappings for that Mapper. What if you want different policies for different mappings within the same Mapper?
- The only condition where this will omit data from the output is when the value is missing from the input. What if you want to omit for other reasons, such as when the value is present but is a blank string? For that, I think you’d need some sort of support in the expression language. Something like $.get(“path”, omit()) or $.getOrOmit(“path”). That adds more flexibility at the cost of relying on EL tricks that some users might find somewhat intimidating.
