Update unit_check.jl

Author: ChrisRackauckas

src/systems/unit_check.jl

@@ -79,7 +79,7 @@ get_unit(x::SciMLBase.NullParameters) = unitless
 get_unit(op::typeof(instream), args) = get_unit(args[1])
 
 function get_unit(op, args) # Fallback
-    result = oneunit(op(get_unit.(args)...))
+    result = op(1 .* get_unit.(args)...)
     try
         get_unit(result)
     catch