final U merge(U oldValue, U newValue) {
        requireNonNull(oldValue, "oldValue");
        requireNonNull(newValue, "newValue");
        final U merged = mergeFunction.apply(oldValue, newValue);
        checkState(merged != null, "mergeFunction must not return null: %s, %s, %s", this, oldValue, newValue);
        return merged;
    }
Merges the specified new option value into the specified old option value.

@param oldValue the old option value.
@param newValue the new option value.
@return the merged option value.
core/src/main/java/com/linecorp/armeria/common/util/AbstractOption.java