What does this error mean?

please, can someone explain to me what this error means?

---- Minecraft Crash Report ----
// Hey, that tickles! Hehehe!

Time: 25.07.21 16:00
Description: Unexpected error

java.lang.NullPointerException: Unexpected error
    at com.flansmod.common.driveables.EntitySeat.func_70106_y(EntitySeat.java:795)
    at net.minecraft.world.World.func_72900_e(World.java:1371)
    at net.minecraft.client.multiplayer.WorldClient.func_72900_e(WorldClient.java:210)
    at net.minecraft.client.multiplayer.WorldClient.func_73028_b(WorldClient.java:291)
    at net.minecraft.client.network.NetHandlerPlayClient.func_147238_a(NetHandlerPlayClient.java:548)
    at net.minecraft.network.play.server.S13PacketDestroyEntities.func_148833_a(SourceFile:42)
    at net.minecraft.network.play.server.S13PacketDestroyEntities.func_148833_a(SourceFile:9)
    at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:212)
    at net.minecraft.client.multiplayer.PlayerControllerMP.func_78765_e(PlayerControllerMP.java:273)
    at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:1602)
    at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:973)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:898)
    at net.minecraft.client.main.Main.main(SourceFile:148)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
    at com.flansmod.common.driveables.EntitySeat.func_70106_y(EntitySeat.java:795)
    at net.minecraft.world.World.func_72900_e(World.java:1371)
    at net.minecraft.client.multiplayer.WorldClient.func_72900_e(WorldClient.java:210)
    at net.minecraft.client.multiplayer.WorldClient.func_73028_b(WorldClient.java:291)
    at net.minecraft.client.network.NetHandlerPlayClient.func_147238_a(NetHandlerPlayClient.java:548)
    at net.minecraft.network.play.server.S13PacketDestroyEntities.func_148833_a(SourceFile:42)
    at net.minecraft.network.play.server.S13PacketDestroyEntities.func_148833_a(SourceFile:9)
    at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:212)
    at net.minecraft.client.multiplayer.PlayerControllerMP.func_78765_e(PlayerControllerMP.java:273)

-- Affected level --
Details:
    Level name: MpServer
    All players: 1 total; [EntityClientPlayerMP['DrKonewka'/254, l='MpServer', x=-425,73, y=7,77, z=364,42]]
    Chunk stats: MultiplayerChunkCache: 4161, 4361
    Level seed: 0
    Level generator: ID 01 - flat, ver 0. Features enabled: false
    Level generator options: 
    Level spawn location: World: (-455,4,379), Chunk: (at 9,0,11 in -29,23; contains blocks -464,0,368 to -449,255,383), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
    Level time: 264269 game time, 6463 day time
    Level dimension: 0
    Level storage version: 0x00000 - Unknown?
    Level weather: Rain time: 0 (now: true), thunder time: 0 (now: false)
    Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
    Forced entities: 99 total; [EntityChicken['Kura'/19, l='MpServer', x=-502,47, y=4,00, z=349,56], EntityCustomNpc['Hitler'/24, l='MpServer', x=-471,50, y=4,00, z=424,50], EntitySheep['Owca'/26, l='MpServer', x=-458,03, y=4,00, z=305,03], EntityItemFrame['entity.ItemFrame.name'/27, l='MpServer', x=-452,50, y=4,50, z=388,06], EntityItemFrame['entity.ItemFrame.name'/28, l='MpServer', x=-451,50, y=4,50, z=388,06], EntityItemFrame['entity.ItemFrame.name'/29, l='MpServer', x=-451,50, y=5,50, z=388,06], EntityItemFrame['entity.ItemFrame.name'/30, l='MpServer', x=-452,50, y=5,50, z=388,06], EntityItemFrame['entity.ItemFrame.name'/31, l='MpServer', x=-453,50, y=4,50, z=388,06], EntityItemFrame['entity.ItemFrame.name'/32, l='MpServer', x=-453,50, y=5,50, z=388,06], EntityVehicle['Panzer38(t) Ausf. A [37mm]'/33, l='MpServer', x=-451,75, y=4,63, z=399,75], EntityVehicle['Opelblitz'/40, l='MpServer', x=-456,02, y=4,63, z=399,81], EntityVehicle['Kubelwagen [MG-34]'/53, l='MpServer', x=-448,17, y=4,63, z=398,98], EntityCustomNpc['Genie'/61, l='MpServer', x=-458,50, y=4,00, z=393,50], EntityWheel['entity.Wheel.name'/323, l='MpServer', x=-282,56, y=4,00, z=358,66], EntityVehicle['FlaK-36 AA-Gun [37mm]'/68, l='MpServer', x=-448,50, y=15,63, z=401,50], EntityWheel['entity.Wheel.name'/324, l='MpServer', x=-282,78, y=4,00, z=360,41], EntityItem['item.item.oakseed'/63561, l='MpServer', x=-471,81, y=4,13, z=407,75], EntityVehicle['FlaK-36 AA-Gun [37mm]'/74, l='MpServer', x=-455,50, y=15,63, z=401,50], EntityCamera['nieznany'/334, l='MpServer', x=-443,50, y=11,63, z=397,50], EntityBat['Nietoperz'/58450, l='MpServer', x=-436,29, y=7,60, z=415,74], EntityBat['Nietoperz'/58451, l='MpServer', x=-437,47, y=5,24, z=397,71], EntityVehicle['PaK-40 [75mm]'/96, l='MpServer', x=-443,50, y=11,63, z=397,50], EntityCustomNpc['Pan Ankin'/102, l='MpServer', x=-445,69, y=15,00, z=395,94], EntityBat['Nietoperz'/108, l='MpServer', x=-427,66, y=9,67, z=413,53], EntityBat['Nietoperz'/109, l='MpServer', x=-402,44, y=6,76, z=389,59], EntityItem['item.item.oakseed'/59245, l='MpServer', x=-441,94, y=4,13, z=422,66], EntityBat['Nietoperz'/110, l='MpServer', x=-372,50, y=4,33, z=370,06], EntityBat['Nietoperz'/111, l='MpServer', x=-376,41, y=6,92, z=405,34], EntityBat['Nietoperz'/113, l='MpServer', x=-367,72, y=9,45, z=357,78], EntityVehicle['FlaK-36 AA-Gun [37mm]'/114, l='MpServer', x=-442,50, y=15,63, z=401,50], EntityBat['Nietoperz'/129, l='MpServer', x=-446,50, y=8,10, z=405,75], EntityBat['Nietoperz'/130, l='MpServer', x=-406,22, y=10,92, z=403,00], EntityBat['Nietoperz'/133, l='MpServer', x=-422,50, y=6,23, z=420,16], EntitySheep['Owca'/135, l='MpServer', x=-419,09, y=4,00, z=295,94], EntityBat['Nietoperz'/138, l='MpServer', x=-398,50, y=10,03, z=427,59], EntityBat['Nietoperz'/139, l='MpServer', x=-370,44, y=8,63, z=409,03], EntityChicken['Kura'/154, l='MpServer', x=-398,53, y=4,00, z=340,47], EntityChicken['Kura'/169, l='MpServer', x=-373,19, y=4,00, z=337,75], EntityChicken['Kura'/176, l='MpServer', x=-346,47, y=2,95, z=427,56], EntityCow['Krowa'/178, l='MpServer', x=-347,06, y=4,00, z=419,84], EntityBat['Nietoperz'/60345, l='MpServer', x=-435,78, y=5,95, z=401,09], EntityBat['Nietoperz'/60346, l='MpServer', x=-458,45, y=7,11, z=388,25], EntityBat['Nietoperz'/58303, l='MpServer', x=-450,48, y=5,02, z=390,68], EntitySeat['entity.Seat.name'/195, l='MpServer', x=-451,94, y=6,25, z=399,81], EntitySeat['entity.Seat.name'/196, l='MpServer', x=-452,07, y=5,06, z=398,43], EntityWheel['entity.Wheel.name'/197, l='MpServer', x=-452,86, y=4,00, z=401,75], EntityWheel['entity.Wheel.name'/198, l='MpServer', x=-450,61, y=4,00, z=401,74], EntityWheel['entity.Wheel.name'/199, l='MpServer', x=-450,64, y=4,00, z=397,74], EntityWheel['entity.Wheel.name'/200, l='MpServer', x=-452,89, y=4,00, z=397,75], EntitySeat['entity.Seat.name'/201, l='MpServer', x=-456,38, y=5,38, z=398,35], EntitySeat['entity.Seat.name'/202, l='MpServer', x=-455,51, y=5,38, z=398,39], EntitySeat['entity.Seat.name'/203, l='MpServer', x=-456,89, y=6,13, z=399,64], EntitySeat['entity.Seat.name'/204, l='MpServer', x=-455,14, y=6,13, z=399,73], EntityItem['item.item.oakseed'/56780, l='MpServer', x=-417,47, y=4,13, z=370,09], EntityCamera['nieznany'/461, l='MpServer', x=-442,50, y=15,63, z=401,50], EntitySeat['entity.Seat.name'/205, l='MpServer', x=-456,95, y=6,13, z=400,82], EntitySeat['entity.Seat.name'/206, l='MpServer', x=-455,20, y=6,13, z=400,91], EntitySeat['entity.Seat.name'/207, l='MpServer', x=-457,01, y=6,13, z=402,01], EntitySeat['entity.Seat.name'/208, l='MpServer', x=-455,26, y=6,13, z=402,10], EntityWheel['entity.Wheel.name'/209, l='MpServer', x=-457,23, y=4,00, z=401,50], EntityWheel['entity.Wheel.name'/210, l='MpServer', x=-454,99, y=4,00, z=401,61], EntityWheel['entity.Wheel.name'/211, l='MpServer', x=-454,77, y=4,00, z=397,37], EntityWheel['entity.Wheel.name'/212, l='MpServer', x=-457,02, y=4,00, z=397,25], EntitySeat['entity.Seat.name'/213, l='MpServer', x=-448,60, y=4,88, z=398,76], EntitySeat['entity.Seat.name'/214, l='MpServer', x=-447,72, y=4,88, z=398,82], EntitySeat['entity.Seat.name'/215, l='MpServer', x=-448,23, y=5,44, z=399,98], EntityWheel['entity.Wheel.name'/216, l='MpServer', x=-449,15, y=4,00, z=400,67], EntityWheel['entity.Wheel.name'/217, l='MpServer', x=-447,40, y=4,00, z=400,77], EntityWheel['entity.Wheel.name'/218, l='MpServer', x=-447,21, y=4,00, z=397,53], EntityWheel['entity.Wheel.name'/219, l='MpServer', x=-448,96, y=4,00, z=397,43], EntitySeat['entity.Seat.name'/220, l='MpServer', x=-449,29, y=16,06, z=399,52], EntityWheel['entity.Wheel.name'/221, l='MpServer', x=-447,65, y=15,00, z=400,48], EntityCamera['nieznany'/477, l='MpServer', x=-448,50, y=15,63, z=401,50], EntityWheel['entity.Wheel.name'/222, l='MpServer', x=-449,40, y=15,00, z=400,52], EntityBat['Nietoperz'/59102, l='MpServer', x=-456,97, y=4,07, z=382,38], EntityCamera['nieznany'/479, l='MpServer', x=-455,50, y=15,63, z=401,50], EntityWheel['entity.Wheel.name'/223, l='MpServer', x=-449,35, y=15,00, z=402,52], EntityWheel['entity.Wheel.name'/224, l='MpServer', x=-447,60, y=15,00, z=402,48], EntitySeat['entity.Seat.name'/225, l='MpServer', x=-456,29, y=16,06, z=399,52], EntityWheel['entity.Wheel.name'/226, l='MpServer', x=-454,65, y=15,00, z=400,48], EntityWheel['entity.Wheel.name'/227, l='MpServer', x=-456,40, y=15,00, z=400,52], EntityWheel['entity.Wheel.name'/228, l='MpServer', x=-456,35, y=15,00, z=402,52], EntityWheel['entity.Wheel.name'/229, l='MpServer', x=-454,60, y=15,00, z=402,48], EntitySeat['entity.Seat.name'/230, l='MpServer', x=-444,11, y=11,31, z=396,98], EntityWheel['entity.Wheel.name'/231, l='MpServer', x=-445,46, y=11,00, z=396,31], EntityWheel['entity.Wheel.name'/232, l='MpServer', x=-445,54, y=11,00, z=398,56], EntityWheel['entity.Wheel.name'/233, l='MpServer', x=-442,29, y=11,00, z=398,66], EntityWheel['entity.Wheel.name'/234, l='MpServer', x=-442,22, y=11,00, z=396,41], EntitySeat['entity.Seat.name'/235, l='MpServer', x=-443,28, y=16,06, z=399,51], EntityWheel['entity.Wheel.name'/236, l='MpServer', x=-441,64, y=15,00, z=400,48], EntityWheel['entity.Wheel.name'/237, l='MpServer', x=-443,39, y=15,00, z=400,51], EntityWheel['entity.Wheel.name'/238, l='MpServer', x=-443,36, y=15,00, z=402,51], EntityWheel['entity.Wheel.name'/239, l='MpServer', x=-441,61, y=15,00, z=402,48], EntityItem['item.item.oakseed'/60659, l='MpServer', x=-434,06, y=4,13, z=418,31], EntityCamera['nieznany'/506, l='MpServer', x=-451,75, y=4,63, z=399,75], EntityCamera['nieznany'/508, l='MpServer', x=-456,02, y=4,63, z=399,81], EntityCamera['nieznany'/510, l='MpServer', x=-448,17, y=4,63, z=398,98], EntityItem['item.item.oakseed'/57598, l='MpServer', x=-413,56, y=8,13, z=376,16], EntityClientPlayerMP['DrKonewka'/254, l='MpServer', x=-425,73, y=7,77, z=364,42]]
    Retry entities: 0 total; []
    Server brand: fml,forge
    Server type: Integrated singleplayer server
Stacktrace:
    at net.minecraft.client.multiplayer.WorldClient.func_72914_a(WorldClient.java:425)
    at net.minecraft.client.Minecraft.func_71396_d(Minecraft.java:2444)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:927)
    at net.minecraft.client.main.Main.main(SourceFile:148)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

-- System Details --
Details:
    Minecraft Version: 1.7.10
    Operating System: Windows 10 (amd64) version 10.0
    Java Version: 1.8.0_51, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 693689072 bytes (661 MB) / 1644167168 bytes (1568 MB) up to 2147483648 bytes (2048 MB)
    JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
    AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
    IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
    FML: MCP v9.05 FML v7.10.99.99 Minecraft Forge 10.13.4.1614 Optifine OptiFine_1.7.10_HD_U_E7 10 mods loaded, 10 mods active
    States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
    UCHIJAAAA    mcp{9.05} [Minecraft Coder Pack] (minecraft.jar) 
    UCHIJAAAA    FML{7.10.99.99} [Forge Mod Loader] (forge-1.7.10-10.13.4.1614-1.7.10.jar) 
    UCHIJAAAA    Forge{10.13.4.1614} [Minecraft Forge] (forge-1.7.10-10.13.4.1614-1.7.10.jar) 
    UCHIJAAAA    customnpcs{1.7.10d} [CustomNpcs] (CustomNPCs_1.7.10d(29oct17).jar) 
    UCHIJAAAA    dynamictrees{1.7.10-0.7.2c} [Dynamic Trees] (DynamicTrees-1.7.10-0.7.2c.jar) 
    UCHIJAAAA    flansmod{@VERSION@} [Flan's Mod Ultimate] (FlansModPlusUltimate1.1-1.7.10.jar) 
    UCHIJAAAA    hidenames{1.1.7} [Hide Names] (Hide+Names-1.7.10-1.1.8.jar) 
    UCHIJAAAA    moreplayermodels{1.7.10b} [MorePlayerModels] (MorePlayerModels_1.7.10b.jar) 
    UCHIJAAAA    harvestcraft{1.7.10j} [Pam's HarvestCraft] (Pam's+HarvestCraft+1.7.10Lb.jar) 
    UCHIJAAAA    worldedit{6.1.1} [WorldEdit] (worldedit-forge-mc1.7.10-6.1.1-dist.jar) 
    GL info: ' Vendor: 'NVIDIA Corporation' Version: '4.6.0 NVIDIA 466.63' Renderer: 'NVIDIA GeForce RTX 2060/PCIe/SSE2'
    Launched Version: 1.7.10-Forge10.13.4.1614-1.7.10
    LWJGL: 2.9.1
    OpenGL: NVIDIA GeForce RTX 2060/PCIe/SSE2 GL version 4.6.0 NVIDIA 466.63, NVIDIA Corporation
    GL Caps: Using GL 1.3 multitexturing.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Anisotropic filtering is supported and maximum anisotropy is 16.
Shaders are available because OpenGL 2.1 is supported.

    Is Modded: Definitely; Client brand changed to 'fml,forge'
    Type: Client (map_client.txt)
    Resource Packs: []
    Current Language: Polski (Polska)
    Profiler Position: N/A (disabled)
    Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
    Anisotropic Filtering: Off (1)
    OptiFine Version: OptiFine_1.7.10_HD_U_E7
    Render Distance Chunks: 32
    Mipmaps: 4
    Anisotropic Filtering: 1
    Antialiasing: 0
    Multitexture: false
    Shaders: null
    OpenGlVersion: 4.6.0 NVIDIA 466.63
    OpenGlRenderer: NVIDIA GeForce RTX 2060/PCIe/SSE2
    OpenGlVendor: NVIDIA Corporation
    CpuCount: 6