### Question:
Schema extends SchemaBase<Schema<T>> { public Schema<T> getChild(NodeId nodeId) { Check.notNull(nodeId, "nodeId"); return children.get(nodeId); } protected  Schema(Builder<T> builder); private  Schema(Builder<T> schemaBuilder, IdentityHashMap<Builder<T>, Schema<T>> schemas); static Builder<T> builder(); T getValue(); Schema<T> getChild(NodeId nodeId); boolean hasChildren(); boolean hasChild(NodeId nodeId);  }### Answer:
@Test(expected = IllegalArgumentException.class) public void builder_get_child_by_null_throws_exception() { new Builder<>().getChild(null); }
@Test(expected = IllegalArgumentException.class) public void schema_get_child_by_null_throws_exception() { new Builder<>().build().getChild(null); }