Assume you have following svg

<svg ...>
<defs>
  <style>
    .cls1 {fill:#1a1a1a}
  </style>
  <path class="cls1" d="..."/>
</defs>

The result is that the style is not applied to the path because the class attribute of the path element is removed. The reason is unconditional removing of all class="" attributes in the svg by this line in the Symbol class

.replaceAll("(class=\").*?(\")", "")

I assume the intention was to remove the class attribute of the svg element and not all class attributes.