Suppose a case class has multiple identifier fields  (non-identifier attributes are elided)
CustomerChatHistory::
    CustomerId : text(20), no default
    ChatNumber : integer, default = 1
    CommentNumber : integer, default = 1
    ...
It's not necessary (or productive) to set default values for case identifier attributes in the model.
Setting the initial identifying values for each new instance is an implementation detail;  the required logic or rules will be expressed in code and/or documented appropriately, as required.
Having declared default values, we cannot use findByCompositeIdentifier() API to locate a case whose identifiers include any default values!
When called, this API checks that values were provided for all caseIdentifier attributes;  it (wrongly) infers that a default-value argument means "not set", so rejects the search attempt.
Symptoms:
JavaScript function findByCompositeIdentifier() fails,with root cause:
cause: javax.script.ScriptException: com.tibco.n2.javascript.WrappedException: Wrapped com.tibco.bds.services.CaseDataAccessFault: com.tibco.bds.common.exception.BDSDAMissingCIDORSearchableAttributeException: BDS DA: Finding by CID an object with composite CIDs requires all CIDs to be specified

Composite Identifier values provided to findByCompositeIdentifier() must not be the Default Value specified for that attribute in the Case Model.

Primary Product Name : TIBCO ActiveMatrix BPM Product Version : 4.1, 4.2, 4.3 Additional Product 1 Name : TIBCO Business Studio - BPM Edition Additional Product Version : 4.1, 4.2, 4.3

Preferred:
1. Remove any default values specified on caseIdentifer attributes of Case Classes
  Note: this is not considered a destructive change.
2. Rebuild & deploy the case model
3. Rebuild & deploy dependent applications
Alternative:
Guard against this in javascript, use alternative API when the lookup is for an item that has any default value:
//...
/* findByCompositeIdriteria does not like model-default values */
if (searchChatNumber!=1 && searchCommentNumber!=1){
    foundRefs= CAC.findByCompositeIdentifier(customerId, searchChatNumber, searchCommentNumber);
}else{
    foundRefs= CAC.findByCriteria('CustomerId="'+customerId+'" and ChatNumber='+searchChatNumber+' and CommentNumber='+searchCommentNumber);
}
//...