DefaultFilterComponentBuilder creates builder attributes for onMatch/onMismatch without performing null checks.

[JWT007]

Log4j 2.24.3

When using a configuration builder and adding a FilterComponentBuilder, generating XML from the ConfigurationBuilder causes exception when the filter is defined with a null OnMatch/OnMismatch Result.

Configuring the onMatch/onMismatch attributes is not required - null should be a valid value.

In this case, no attributtes should be added.

However in tthe DefaulttFilterComponentBuilder, attributes are added to tthe builder without performing a null-check first.

class DefaultFilterComponentBuilder extends DefaultComponentAndConfigurationBuilder<FilterComponentBuilder>
        implements FilterComponentBuilder {

    public DefaultFilterComponentBuilder(
            final DefaultConfigurationBuilder<? extends Configuration> builder,
            final String type,
            final String onMatch,
            final String onMismatch) {
        super(builder, type);
        addAttribute(AbstractFilterBuilder.ATTR_ON_MATCH, onMatch);
        addAttribute(AbstractFilterBuilder.ATTR_ON_MISMATCH, onMismatch);
    }
}

This results attributes with null values in the builder tree which can cause XML serialization problems.

I think this might be better:

class DefaultFilterComponentBuilder extends DefaultComponentAndConfigurationBuilder<FilterComponentBuilder>
        implements FilterComponentBuilder {

    public DefaultFilterComponentBuilder(
            final DefaultConfigurationBuilder<? extends Configuration> builder,
            final String type,
            final String onMatch,
            final String onMismatch) {
        super(builder, type);
        Optional.ofNullable(onMatch).ifPresent(() -> addAttribute(AbstractFilterBuilder.ATTR_ON_MATCH, onMatch));
        Optional.ofNullable(onMismatch).ifPresent(() -> addAttribute(AbstractFilterBuilder.ATTR_ON_MISMATCH, onMismatch));
    }
}

[ppkarwasz]

I am closing this as duplicate of #2791.