[jira] Created: (TAPESTRY-1928) Coercion from null to Boolean yields false instead of null

[Geoff Callender (JIRA)]

Coercion from null to Boolean yields false instead of null
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                 Key: TAPESTRY-1928
                 URL: https://issues.apache.org/jira/browse/TAPESTRY-1928
             Project: Tapestry
          Issue Type: Bug
          Components: tapestry-ioc
    Affects Versions: 5.0.6
            Reporter: Geoff Callender


Boolean has 3 states: null, true, false, but the coercer coerces null to false. 
 While this is correct behaviour for the boolean primitive (which has only 2 
states), it is not correct for Boolean.

The same argument applies here as in TAPESTRY-1648 which dealt with null 
BigDecimal and Integer.

A practical consequence is that a BooleanValueEncoder that is 3-value aware 
becomes useless because the coercer will override it.  

For example I combined a BooleanValueEncoder with Select to allow a user to 
choose between "", "true", and "false".  But when the user chooses "", they 
unexpectedly get the same result as choosing "false".  Here's the template code:

        <select t:id="active" t:type="Select" value="active" model="actives" 
encoder="booleanValueEncoder"/>

Here's the relevant java:

        static private final Boolean[] ACTIVES = { null, Boolean.TRUE, 
Boolean.FALSE };
        static private final BooleanValueEncoder BOOLEAN_VALUE_ENCODER = new 
BooleanValueEncoder();

        public Boolean getActive() {
                return _active;
        }

        public  void setActive(Boolean active) {
                _active = active;
        }

        public Boolean[] getActives() {
                return ACTIVES;
        }
        
        public BooleanValueEncoder getBooleanValueEncoder() {
                return BOOLEAN_VALUE_ENCODER;
        }

Here's a BooleanValueEncoder:

public class BooleanValueEncoder implements ValueEncoder<Boolean> {

        public String toClient(Boolean value) {
                return value == null ? "" : value.toString();
        }

        public Boolean toValue(String clientValue) {
                return clientValue.equals("") ? null : 
Boolean.valueOf(clientValue);
        }

}

When the user chooses "", Tapestry calls setActive(Boolean.FALSE) instead of 
setActive(null).

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