Repository: PaperMC/Paper
File: paper-api/src/main/java/org/bukkit/entity/HumanEntity.java (Java)

Code before:
     * @param sign The sign to open
     * @param side The side of the sign to open
     */
    void openSign(org.bukkit.block.@NotNull Sign sign, org.bukkit.block.sign.@NotNull Side side);
    // Paper end

    /**
     * Make the entity drop the item in their hand.
     * <br>
     * This will force the entity to drop the item they are holding with
     * an option to drop the entire {@link ItemStack} or just 1 of the items.
     *
     * @deprecated You should instead use {@link #dropItem(EquipmentSlot, int)} with a {@link EquipmentSlot#HAND} parameter.
     * @param dropAll True to drop entire stack, false to drop 1 of the stack
     * @return True if item was dropped successfully
     */
    @Deprecated
    public boolean dropItem(boolean dropAll);

    /**
     * Makes the entity drop an item from their inventory based on the slot.
     *
     * @param slot   The slot to drop
     * @param amount The number of items to drop from this slot. Values below 1 don't drop an Item
     * @return The dropped item entity, or null if the action was unsuccessful
     * @throws IndexOutOfBoundsException If the slot is negative or bigger than the player's inventory
     */
    public @Nullable Item dropItem(int slot, int amount);

    /**
     * Makes the player drop an item from their inventory based on the equipment slot.
     *
     * @param slot   The equipment slot to drop
     * @param amount The amount of items to drop from this equipment slot. Values below 1 don't drop an Item
     * @return The dropped item entity, or null if the action was unsuccessful
     */
    public @Nullable Item dropItem(@NotNull EquipmentSlot slot, int amount);

    /**
     * Makes the entity drop an item from their inventory based on the slot.
     * Instead of the item being dropped where the player is currently looking, this method makes it drop in
     * a random direction, similar to how items are dropped after a player's death.
     *
     * @param slot   The slot to drop
     * @param amount The number of items to drop from this slot. Values below 1 don't drop an Item
     * @return The dropped item entity, or null if the action was unsuccessful
     * @throws IndexOutOfBoundsException If the slot is negative or bigger than the player's inventory
     */
    public @Nullable Item dropItemRandomly(int slot, int amount);

    /**

Review comment (suggestion):
I think I'd prefer just a standard IllegalArgumentException for an "invalid slot". That is more flexible for the future if slot numbers are ever non-contiguous. 

Code after:
     *
     * @param sign The sign to open
     * @param side The side of the sign to open
     */
    void openSign(org.bukkit.block.@NotNull Sign sign, org.bukkit.block.sign.@NotNull Side side);
    // Paper end

    /**
     * Make the entity drop the item in their hand.
     * <br>
     * This will force the entity to drop the item they are holding with
     * an option to drop the entire {@link ItemStack} or just 1 of the items.
     *
     * @param dropAll True to drop entire stack, false to drop 1 of the stack
     * @return True if item was dropped successfully
     * @apiNote You should instead use {@link #dropItem(EquipmentSlot, int)} or {@link #dropItem(EquipmentSlot)} with a {@link EquipmentSlot#HAND} parameter.
     */
    @ApiStatus.Obsolete(since = "1.21.4")
    boolean dropItem(boolean dropAll);

    /**
     * Makes the player drop all items from their inventory based on the inventory slot.
     *
     * @param slot the equipment slot to drop
     * @return the dropped item entity, or null if the action was unsuccessful
     */
    @Nullable
    default Item dropItem(final int slot) {
        return this.dropItem(slot, Integer.MAX_VALUE);
    }

    /**
     * Makes the player drop an item from their inventory based on the inventory slot.
     *
     * @param slot   the slot to drop
     * @param amount the number of items to drop from this slot. Values below one always return null
     * @return the dropped item entity, or null if the action was unsuccessful
     * @throws IllegalArgumentException if the slot is negative or bigger than the player's inventory
     */
    @Nullable
    default Item dropItem(final int slot, final int amount) {
        return this.dropItem(slot, amount, false, null);
    }

    /**
     * Makes the player drop an item from their inventory based on the inventory slot.
     *
     * @param slot            the slot to drop
     * @param amount          the number of items to drop from this slot. Values below one always return null
     * @param throwRandomly   controls the randomness of the dropped items velocity, where {@code true} mimics dropped
     *                        items during a player's death, while {@code false} acts like a normal item drop.