when i add a 3dtiles url in the ue4 ,zhe error comes out.
i need help
The error stems from this line.
According to the 3d tiles specificaction, the geometricError is required for each tile. So strictly speaking, the tileset that you are loading is invalid.
Which tool are you using to create the tileset? (You might consider adding the geometricError manually, but depending on the size of the tileset, that may be more or less feasible…)
The source of the data is also a problem for me, I only know that it is obtained from the skyline data type conversion. 
I raised https://github.com/CesiumGS/cesium-native/issues/343 for that. I think in this case, it could be reasonable to still allow the data to be loaded (CesiumJS does it, and “only” prints a warning), but there has not been a decision yet.