Compiler complaining about code that can't be reached, builtin types .equals()

[Sean Grimes via Digitalmars-d-learn]

I have a method, containsValue() in a class similar to 
java.util.HashMap.
The class is a template class, instantiated with 2 parameters, K 
key, V value.

bool containsValue(V value){

     // dlang associative array, .values returns dynamic array of 
values in the aa
     auto values = this.internal_arr.values;

      /*
       * isBuiltIn() checks against all the builtin types in D
       * returns true if value instantiated as int, double, 
immutable(char)[] etc...
       * returns false iff value is a user defined object
       */
     if(!isBuiltIn(value)){
         foreach(val; values){
             if(val.equals(value))
	        return true;
         }
     }

     // isBuiltin() false, assume builtin type, use "==" for 
comparison
     else{
         foreach(val; values){
             if(val == value)
                 return true;
        }
     }
     return false;
}

The problem I'm having is using a D builtin type for the value 
parameter. The compiler tells me "no property 'equals' for type 
'string'" in the containsValue() method. Well that's well and 
good, but I already know that which is why I check if the class 
has been instantiated with a builtin type or a user defined type.

My question: Is there any way around the compiler complaining 
about this? The code doesn't allow (as best I can tell) the 
.equals() method to be called when "value" is a builtin type, so 
why does the compiler still complain?

As a side note, I couldn't get std.traits.isBuiltinType(T) to 
work, so the function isBuiltIn() is not just calling 
std.traits.isBuiltinType(T), it's checking the typeid(value) 
against D builtin typeids.