code: public String buildStyleClassValue(List/*<String>*/ styleClasses) {
          if(styleClasses == null)
              return EMPTY;
  
          boolean styleWritten = false;
          InternalStringBuilder buf = new InternalStringBuilder();
          for(int i = 0; i < styleClasses.size(); i++) {
              if(styleWritten)
                  buf.append(SPACE);
  
              if(styleClasses.get(i) != null) {
                  buf.append(styleClasses.get(i));
                  styleWritten = true;
              }
          }
  
          if(!styleWritten)
              return null;
          else return buf.toString();
      }
docs: Build the value of the HTML style class attribute from the {@link List} of style classes.  The style classes
  are converted into a string in their list order.  For example, a list with contents:
  <pre>
  foo,bar,baz
  </pre>
  will be convereted into a style class whose value is <code>foo,bar,baz</code>
  
  @param styleClasses the classes to render into a style class value
  @return the string style class or an empty string if no style classes are provided