Fluent API addition request

Hi All

I really like the fluent style in Cayenne 4.

However I found that sometimes the fluent style in my code needs to be  
interrupted if some condition has to be tested before configuring the  
select any further, which then breaks the nice flow of code.

So I suggest adding the following API to ObjectSelect and to Expression  
that'll smooth this over:

Add to ObjectSelect:
     /**
      * Conditionally append/chain the provided operation.
      * @param condition if true then accept is invoked on the Consumer  
parameter
      * @param op provides the ObjectSelect to be modified if condition is  
true
      * @return
      */
     public ObjectSelect addIf( boolean condition, Consumer> op )
     {
         if ( condition ) op.accept( this );
         return this;
     }
Examples from my code base:
     .addIf( yearRange != null, q -> q.where( APPOINTMENT_DATE.gt(  
yearRange ) ) )


     .addIf( includePublic, q -> q.or( createDateRangeExpression( 9999 ) ) )


     .addIf( withAttachments, q -> q.prefetch( Message.ATTACHMENTS.joint()  
) )

----------------------

Add to Expression:
     /**
      * Conditionally append the provided operation to the current  
expression.
      * @param condition if true then apply is invoked on the UnaryOperator  
parameter
      * @param op provides the expression to be modified if condition is  
true
      * @return
      */
     public Expression addIf( boolean condition, UnaryOperator op )
     {
         return (condition) ? op.apply( this ) : this;
     }
Examples from my code base:
     DefaultValue.USER.eq( userId ).andExp( DefaultValue.VALUE.ne( "" ) )
     .addIf( keyName != null, exp -> exp.andExp( DefaultValue.NAME.eq(  
keyName ) ) )


     ExpressionFactory.matchExp( PatientNew.DATE_OF_BIRTH_PROPERTY, dob )
     .addIf( idNo.length() > 6, exp -> exp.andExp( PatientNew.ID_NO.like(  
idNo.substring(0,6)+"%" ) ) )


     User.FIRSTNAME.eq( userParts[0] )
     .addIf( userParts.length == 2, exp -> exp.andExp( User.SURNAME.eq(  
userParts[1] ) ) )


     AppointmentSms.APPOINTMENT_DATE.eq( aptDate )
     .addIf( marketing, q -> q.andExp( AppointmentSms.MARKETING.eq( true )  
) )

What do you guys think ?

I can submit a PR if it passes as a good feature to add.
The name of the method can be changed if anyone has a better suggestion.

Thanks, regards
Jurgen