Remove the default constructor in at connector

Author: YingboMa

src/systems/abstractsystem.jl

@@ -593,7 +593,9 @@ function with_connection_type(expr)
     args = sig.args[2:end]
 
     quote
-        struct $fname end
+        struct $fname
+            $(gensym()) -> 1 # this removes the default constructor
+        end
         function $fname($(args...))
             function f()
                 $body

src/systems/diffeqs/sdesystem.jl

@@ -83,7 +83,7 @@ function SDESystem(deqs::AbstractVector{<:Equation}, neqs, iv, dvs, ps;
                    default_u0=Dict(),
                    default_p=Dict(),
                    defaults=_merge(Dict(default_u0), Dict(default_p)),
-                   name = gensym(:SDESystem)
+                   name = gensym(:SDESystem),
                    connection_type=nothing,
                    )
     iv′ = value(iv)

src/systems/jumps/jumpsystem.jl

@@ -59,7 +59,7 @@ function JumpSystem(eqs, iv, states, ps;
                     default_u0=Dict(),
                     default_p=Dict(),
                     defaults=_merge(Dict(default_u0), Dict(default_p)),
-                    name = gensym(:JumpSystem)
+                    name = gensym(:JumpSystem),
                     connection_type=nothing,
                     )