allow multibody frame connectors to be unbalanced

Author: baggepinnen

src/systems/connectors.jl

@@ -47,7 +47,7 @@ function connector_type(sys::AbstractSystem)
     if n_flow == 1 && length(sts) == 1
         return DomainConnector()
     end
-    if n_flow != n_regular
+    if n_flow != n_regular && !isframe(sys)
         @warn "$(nameof(sys)) contains $n_flow flow variables, yet $n_regular regular " *
               "(non-flow, non-stream, non-input, non-output) variables. " *
               "This could lead to imbalanced model that are difficult to debug. " *