openrtb-core/src/main/java/com/google/openrtb/json/AbstractOpenRtbJsonWriter.java
protected final void writeContentCategories(
      String fieldName, List<String> cats, JsonGenerator gen)
      throws IOException {
    if (!cats.isEmpty()) {
      gen.writeArrayFieldStart(fieldName);
      for (String cat : cats) {
        writeContentCategory(cat, gen);
      }
      gen.writeEndArray();
    }
  }
protected final void writeContentCategories(
      String fieldName, List<String> cats, JsonGenerator gen)
      throws IOException {
    if (!cats.isEmpty()) {
      gen.writeArrayFieldStart(fieldName);
      for (String cat : cats) {
        writeContentCategory(cat, gen);
      }
      gen.writeEndArray();
    }
  }
Writes an array of ContentCategory if not empty.

@see #writeContentCategory(String, JsonGenerator)