public final void writeBooleanNull() {
        if ((this.context.features & (MASK_NULL_AS_DEFAULT_VALUE | WriteNullBooleanAsFalse.mask)) != 0) {
            writeBool(false);
        } else {
            writeNull();
        }
    }
If ReferenceDetection has been set, returns the path of the current object, otherwise returns null
@since 2.0.51
@return the path of the current object
core/src/main/java/com/alibaba/fastjson2/JSONWriter.java