Just error if an equation only contains parameters (and no variables)

Author: hersle

src/utils.jl

@@ -186,13 +186,8 @@ function check_equations(eqs, iv)
 
     for eq in eqs
         vars, pars = collect_vars(eq, iv)
-        if isempty(vars)
-            if isempty(pars)
-                throw(ArgumentError("Equation $eq contains no variables or parameters."))
-            else
-                throw(ArgumentError("Equation $eq contains only parameters, but relationships between parameters should be specified with defaults or parameter_dependencies."))
-            end
-        end
+        isempty(vars) && !isempty(pars) && 
+            throw(ArgumentError("Equation $eq contains only parameters, but relationships between parameters should be specified with defaults or parameter_dependencies."))
     end
 end
 """

test/odesystem.jl

@@ -427,7 +427,6 @@ eqs = [
 @parameters p q
 @test_throws ArgumentError ODESystem([p ~ q], t; name = :foo)
 @test_throws ArgumentError ODESystem([p ~ 1], t; name = :foo)
-@test_throws ArgumentError ODESystem([1 ~ 2], t; name = :foo)
 
 @variables x(t)
 @parameters M b k