public Builder setCollapseUnknowns(boolean collapseUnknowns) {
            this.collapseUnknowns = collapseUnknowns;
            return this;
        }
Sets whether consecutive unknown character should be collapsed into one large unknown token (default)
or be returned as single character tokens.
linguistics-components/src/main/java/com/yahoo/language/sentencepiece/SentencePieceEmbedder.java