What I noticed
I ran into a question recently around empty strings in Connect CDC, and it looks simple on the surface. But once I dug into it, there is a subtle behavior that can affect downstream systems.
How CDC handles empty strings
In a bi-directional setup between IBM i and Oracle:
- Empty strings are replicated as empty values by default
- CDC does not automatically convert them to NULL
So if a source column has an empty string, the target will also receive an empty string.
Why this matters more than it seems
This becomes important when the target database treats empty strings differently.
For example:
- Some Oracle configurations treat empty strings as NULL
- Application logic may expect NULL instead of an empty value
So even though CDC is doing exactly what it should, the behavior at the target can look inconsistent.
What to check on the Oracle side
I usually check two things:
- Schema definition for CHAR and VARCHAR columns
- Application logic that reads the data
If those expect NULL but CDC is sending empty strings, it can lead to subtle bugs or unexpected query results.
When transformations are needed
If the requirement is to treat empty strings as NULL, this needs to be handled explicitly.
That means adding a transformation in the CDC mapping layer to convert:
'' → NULL
CDC will not do this automatically.
What changed for me
Before this, I assumed empty vs NULL was just a database detail.
This made it clear that CDC preserves exactly what the source sends, and it is up to the model or application to interpret it correctly.
Takeaway
Connect CDC does replicate empty strings. The real question is how the target system interprets them.
If empty and NULL mean different things in your system, this is something worth handling early in the design.
References
- Connect CDC knowledge base - empty string replication behavior
- Connect CDC mapping documentation - transformations and data handling
Have you run into cases where empty strings caused unexpected behavior in your target system?
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Adhitya Maya
*Precisely Software Inc.
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