Generating an invalid puml due to the @ prefix

[shiena]

steps to reproduce:

1. Prepare the source file including the @ prefix

   @startuml
   class @ClassA{
           public @IList<@string> @Strings{get;} = new @List<@string>();
               public @Type1 @Prop1{get;set;}
                   public @Type2 @field1;
   }
   
   class @Type1 {
           public @int @value1{get;set;}
   }
   
   class @Type2{
           public @string @string1{get;set;}
               public @ExternalType @Prop2 {get;set;}
   }
   @enduml

2. Generating .puml with puml-gen

   $ puml-gen .\input.cs -createAssociation

   @startuml
   class @ClassA {
   }
   class @Type1 {
   }
   class @Type2 {
   }
   class "@IList`1"<T> {
   }
   @ClassA o-> "@Strings<@string>" "@IList`1"
   @ClassA --> "@Prop1" @Type1
   @ClassA --> "@field1" @Type2
   @Type1 --> "@value1" @int
   @Type2 --> "@string1" @string
   @Type2 --> "@Prop2" @ExternalType
   @enduml

3. Generating .png with plantuml

   plantuml input.puml

4. The generated .puml contains an error

   Error line 10 in file: input.puml
   Some diagram description contains errors