handle empty arrays

Author: baggepinnen

src/named_systems2.jl

@@ -899,7 +899,7 @@ function names2indices(name::Symbol, allnames)
 end
 
 function ExtendedStateSpace(P::NamedStateSpace; z=P.y, y=P.y, w=P.u, u=P.u)
-    ExtendedStateSpace(P, w, u, z, y)
+    ExtendedStateSpace(P, isempty(w) ? Symbol[] : w, isempty(u) ? Symbol[] : u, isempty(z) ? Symbol[] : z, isempty(y) ? Symbol[] : y)
 end
 
 """

test/test_named_systems2.jl

@@ -160,7 +160,7 @@ s2 = named_ss(G2, x = :z, u = :u2, y=:y2)
 @test_nowarn check_all_unique(s1, s2)
 
 s1e = ExtendedStateSpace(s1, y=s1.y, u=s1.u, z=[], w=[])
-@test s1.sys == system_mapping(s1e)
+@test s1.sys == system_mapping(s1e).sys
 @test ss(s1e) == ss(s1)
 
 s1d = c2d(s1, 1.0)