#Bug

The BuilderDemo is a simple demo for a bug hitting me when using @Builder annotation.

It appears (a NPE in ArrayList.addAll) when I use the toBuilder() method of an instance containing a null SINGULARIZED collection( or map).

Note : if I remove the @Singular annotation, the NPE is not thrown (see should_not_NPE_on_NOT_singularized_item_when_using_toBuilder_from_an_instance_created_with_a_null_collection)

Test stack trace :

java.lang.NullPointerException
    at java.util.ArrayList.addAll(ArrayList.java:577)
    at BuilderDemo$BuilderDemoBuilder.singularNames(BuilderDemo.java:51)
    at BuilderDemo.toBuilder(BuilderDemo.java:100)
    at BuilderDemoTest.should_not_NPE_on_singularized_item_when_using_toBuilder_from_an_instance_created_with_a_null_collection(BuilderDemoTest.java:21)

Generated source code (thx delombok plugin)

    @SuppressWarnings("all")
    @javax.annotation.Generated("lombok")
    public BuilderDemoBuilder singularNames(final java.util.Collection<? extends String> singularNames) {
        if (this.singularNames == null) this.singularNames = new java.util.ArrayList<String>();
        this.singularNames.addAll(singularNames);
        return this;
    }

the NPE is thrown at line this.singularNames.addAll(singularNames); : the singularNames parameter is null, and ArrayList.addAll does not support null param.

See #src/test/java/BuilderDemoTest.java