@Nullable
    public final Double getDoubleAndRemove(IN_NAME name) {
        return contains(name) ? setters().getDoubleAndRemove(name) : null;
    }
Makes the current {@link #delegate()} a new {@link #parent()} and clears the current {@link #delegate()}.
Call this method when you create a new object derived from the {@link #delegate()},
so that any further modifications to this builder do not break the immutability of the created object.

@return the {@link #delegate()}
core/src/main/java/com/linecorp/armeria/common/StringMultimapBuilder.java