InternalModel error if ym keyword argument is absent with moveinput!

Author: franckgaga

docs/src/manual/linmpc.md

@@ -82,7 +82,7 @@ for details).
 
 [^1]: We could have use an [`InternalModel`](@ref) structure with
     `mpc = LinMPC(InternalModel(model), Hp=15, Hc=2, Mwt=[1, 1], Nwt=[0.1, 0.1])` to avoid
-    state estimator design . It was tested on the example of this page and it gives similar
+    state estimator design . It was tested on the example of this page and it gives similar 
     results.
 
 Before closing the loop, we call [`initstate!`](@ref) with the actual plant inputs and

src/predictive_control.jl

@@ -389,6 +389,8 @@ end
 Use current measured outputs `ym` for prediction when `estim` is a [`InternalModel`](@ref).
 """
 function predictstoch!(mpc, estim::InternalModel, d, ym )
+    isnothing(ym) && error("Predictive controllers with InternalModel need the measured "*
+                           "outputs ym in keyword argument to compute control actions u")
     ŷd = h(estim.model, estim.x̂d, d - estim.model.dop) + estim.model.yop 
     ŷs = zeros(estim.model.ny)
     ŷs[estim.i_ym] = ym - ŷd[estim.i_ym]  # ŷs=0 for unmeasured outputs