code: private JClassType extractParameterizedType( String clazz, JParameterizedType parameterizedType ) throws UnableToCompleteException {
          if ( parameterizedType == null ) {
              logger.log( TreeLogger.Type.ERROR, "Expected the " + clazz + " declaration to specify a parameterized type." );
              throw new UnableToCompleteException();
          }
          JClassType[] typeParameters = parameterizedType.getTypeArgs();
          if ( typeParameters == null || typeParameters.length != 1 ) {
              logger.log( TreeLogger.Type.ERROR, "Expected the " + clazz + " declaration to specify 1 parameterized type." );
              throw new UnableToCompleteException();
          }
          return typeParameters[0];
      }
docs: Extract the parameter's type.
  
  @param clazz the name of the interface
  @param parameterizedType the parameterized type
  
  @return the extracted type
  @throws UnableToCompleteException if the type contains zero or more than one parameter