Error on graph fragments with no way to initialize (no priors) with bad error message

[Affie]

using IncrementalInference

fg = initfg()

addVariable!(fg, :x0, ContinuousScalar)
addFactor!(fg, [:x0], Prior(Normal(1.0,0.1)))

addVariable!(fg, :x1, ContinuousScalar)

addVariable!(fg, :x2, ContinuousScalar)
addFactor!(fg, [:x1,:x2], LinearRelative(Normal(1.0,0.1)))

solveGraph!(fg)

Error:

    nested task error: CSM-4a unknown status root NULL
    Stacktrace:
     [1] error(s::String)
       @ Base ./error.jl:33
     [2] preDownSolve_StateMachine(csmc::CliqStateMachineContainer{BayesTreeNodeData, GraphsDFG{SolverParams, DFGVariable, DFGFactor}, GraphsDFG{SolverParams, DFGVariable, DFGFactor}, MetaBayesTree})
       @ IncrementalInference ~/.julia/packages/IncrementalInference/yEZz4/src/CliqueStateMachine.jl:615
     [3] (::StateMachine{CliqStateMachineContainer})(userdata::CliqStateMachineContainer{BayesTreeNodeData, GraphsDFG{SolverParams, DFGVariable, DFGFactor}, GraphsDFG{SolverParams, DFGVariable, DFGFactor}, MetaBayesTree}, timeout::Nothing; pollinterval::Float64, breakafter::Function, verbose::Bool, verbosefid::Base.TTY, verboseXtra::IncrementalInference.CliqStatus, iterlimit::Int64, injectDelayBefore::Nothing, recordhistory::Bool, housekeeping_cb::IncrementalInference.var"#477#479"{IncrementalInference.TreeClique, CliqStateMachineContainer{BayesTreeNodeData, GraphsDFG{SolverParams, DFGVariable, DFGFactor}, GraphsDFG{SolverParams, DFGVariable, DFGFactor}, MetaBayesTree}})
       @ FunctionalStateMachine ~/.julia/packages/FunctionalStateMachine/2JZFG/src/StateMachine.jl:82
     [4] initStartCliqStateMachine!(dfg::GraphsDFG{SolverParams, DFGVariable, DFGFactor}, tree::MetaBayesTree, cliq::IncrementalInference.TreeClique, timeout::Nothing; oldcliqdata::BayesTreeNodeData, verbose::Bool, verbosefid::Base.TTY, drawtree::Bool, show::Bool, incremental::Bool, limititers::Int64, upsolve::Bool, downsolve::Bool, recordhistory::Bool, delay::Bool, logger::Base.CoreLogging.SimpleLogger, solve_progressbar::ProgressMeter.ProgressUnknown, algorithm::Symbol, solveKey::Symbol)
       @ IncrementalInference ~/.julia/packages/IncrementalInference/yEZz4/src/CliqueStateMachine.jl:64
     [5] tryCliqStateMachineSolve!(dfg::GraphsDFG{SolverParams, DFGVariable, DFGFactor}, treel::MetaBayesTree, cliqKey::Int64, timeout::Nothing; oldtree::MetaBayesTree, verbose::Bool, verbosefid::Base.TTY, drawtree::Bool, limititers::Int64, downsolve::Bool, incremental::Bool, delaycliqs::Vector{Symbol}, recordcliqs::Vector{Symbol}, solve_progressbar::ProgressMeter.ProgressUnknown, algorithm::Symbol, solveKey::Symbol)
       @ IncrementalInference ~/.julia/packages/IncrementalInference/yEZz4/src/SolverAPI.jl:112
     [6] (::IncrementalInference.var"#528#531"{MetaBayesTree, Bool, Bool, Base.TTY, Bool, Bool, Vector{Symbol}, Vector{Symbol}, Symbol, Symbol, GraphsDFG{SolverParams, DFGVariable, DFGFactor}, MetaBayesTree, Nothing, ProgressMeter.ProgressUnknown, Int64, Int64})()
       @ IncrementalInference ./task.jl:423

[Affie]

Btw, initializing x1(or x2) with initManual!, stops the error.