Placed duct/duct-junction adjacent to small pipe or storage tank

Version: 0.17.79 (build 47865, win64)
FMF Version 1.1.0

Other mods:
Krastorio & Dependencies,
Space Exploration & Dependencies

The mod Fluid Must Flow caused a non-recoverable error.
Please report this error to the mod author.

Error while running event FluidMustFlow::on_built_entity (ID 6)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
FluidMustFlow/control.lua:457: in function 'endpointOnBuildRightFacing'
FluidMustFlow/control.lua:533: in function <FluidMustFlow/control.lua:525>
stack traceback:
[C]: in function 'index'
__FluidMustFlow/control.lua:457: in function 'endpointOnBuildRightFacing'
FluidMustFlow/control.lua:533: in function <FluidMustFlow/control.lua:525>

Thanks for ur report, should be fixed in the latest version (1.1.1).

Not fixed, same issue:

Upon further investigation I've found that the game does not crash when a normal pipe is placed adjacent to an existing duct, but placing a duct next to an existing pipe does. This is also the case for storage tanks. Interestingly, when a normal pipe (or storage tank) is placed adjacent to an existing duct the duct is deleted, and a duct-placement warning message appears.

Version: 0.17.79 (build 47865, win64)
FMF Version 1.1.1

Error while running event FluidMustFlow::on_built_entity (ID 6)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
FluidMustFlow/control.lua:452: in function 'endpointOnBuildRightFacing'
FluidMustFlow/control.lua:529: in function <FluidMustFlow/control.lua:521>
stack traceback:
[C]: in function 'index'
__FluidMustFlow/control.lua:452: in function 'endpointOnBuildRightFacing'
FluidMustFlow/control.lua:529: in function <FluidMustFlow/control.lua:521>

I believe the solution requires handlers for multiple events including attempting to place duct adjacent to normal pipe networks (cannot place--give warning message), and attempting to place a normal pipe or storage tank adjacent to a duct network (cannot place--give different warning message). There may be more situations that I can't think of at the moment

I have try this error many time but in single player seems unreproducible (I suppose that u got this in multyplayer so),
I will try to encapsulate the validation of entity better but I don't know how to it for sure, because on API isn't explaned the right way how check if an entity is valid, and I check it always before do operation on an entity, anyway if check if an entity is valid is an "LuaEntity API call when LuaEntity was invalid." error, I'm in a loop that I can't solve.

If u think to know how solve this bug u are free to make ur modification to control.lua code and send it to me

I'm not a mod developer; I can't diagnose the issue for you, sorry. I love the concept of this mod and hope it gets fixed eventually. I've included my entire mod list bellow if that helps any :s

[I've been having this issue in singleplayer. I haven't tried FMF in multiplayer]

As of 12/12/19 all of the following mods are up to date for Factorio version 0.17.79:
Alien Biomes 0.4.16
Avoid Struggle with Integration Libary (Alpha) 0.5.17
Bullet Trails 0.4.1
Deadlock's Stacking Beltboxes & Compact Loaders 2.2.2
Even Distribution 0.3.13
Factorio Standard Libary 1.3.0
Factory Planner 0.17.73
Fluid Must Flow 1.1.1
Krastorio Graphics 0.1.8
Krastorio Legacy 1.4.45
LTN - Logistic Train Network 1.11.7
LTN Combinator 0.5.3
Max Rate Calculator 3.2.30
Nanobots: Early Bots 3.1.0
Optera's Libary 0.1.8
Robot Attrition 0.3.8
Space Exploration 0.1.149
Space Exploration Graphics (Required) 0.1.47
Space Exploration Postprocess (Required) 0.1.44

I will try to fix this.
If u have a way to reproduce for sure the error in ur savegame, could be very helpuful have the savegame file and a procedure of how reproduce the bug.

reproduced this (also 1.1.1) using a non-return duct coming off a Schall's +2 storage tank with outtake. it didn't happen til I rotated the entity right and had it up against the input of the tank.

196169.510 Error MainLoop.cpp:1195: Exception at tick 88047384: The mod Fluid Must Flow caused a non-recoverable error.
Please report this error to the mod author.

Error while running event FluidMustFlow::on_built_entity (ID 6)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
FluidMustFlow/control.lua:452: in function 'endpointOnBuildRightFacing'
FluidMustFlow/control.lua:529: in function <FluidMustFlow/control.lua:521>
stack traceback:
[C]: in function 'index'
__FluidMustFlow/control.lua:452: in function 'endpointOnBuildRightFacing'
FluidMustFlow/control.lua:529: in function <FluidMustFlow/control.lua:521>
196169.510 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "The mod Fluid Must Flow caused a non-recoverable error.
Please report this error to the mod author.

Error while running event FluidMustFlow::on_built_entity (ID 6)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
FluidMustFlow/control.lua:452: in function 'endpointOnBuildRightFacing'
FluidMustFlow/control.lua:529: in function <FluidMustFlow/control.lua:521>
stack traceback:
[C]: in function 'index'
__FluidMustFlow/control.lua:452: in function 'endpointOnBuildRightFacing'
FluidMustFlow/control.lua:529: in function <FluidMustFlow/control.lua:521>"
196169.510 Info ServerMultiplayerManager.cpp:776: updateTick(88047384) changing state from(InGame) to(Failed)
196169.510 Quitting: multiplayer error.
196169.995 Info ServerMultiplayerManager.cpp:138: Quitting multiplayer connection.
196169.995 Info ServerMultiplayerManager.cpp:776: updateTick(4294967295) changing state from(Failed) to(Closed)
196170.063 Info UDPSocket.cpp:218: Closing socket
196170.063 Info UDPSocket.cpp:248: Socket closed
196170.064 Goodbye

Same here: crashed when placing a single duct between Schall's "Boilers+1"

Should be fixed in the latest version (1.2.2).

Cool! Thank you very much!

This time the credit of this go to iicyan, I have "hire" him as mod maintainer