public final SELF sizeHint(int sizeHint) {
        checkArgument(sizeHint >= 0, "sizeHint: %s (expected: >= 0)", sizeHint);
        checkState(delegate == null, "sizeHint cannot be specified after a modification is made.");
        this.sizeHint = sizeHint;
        return self();
    }
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