Replacing surrogates chars by html entities

gistfile1.groovy

@Grapes(
    @Grab(group='commons-lang', module='commons-lang', version='2.6')
)

/*@Grapes(
    @Grab(group='org.apache.commons', module='commons-lang3', version='3.3')
)*/

 
import org.apache.commons.lang.StringEscapeUtils
//import org.apache.commons.lang3.StringEscapeUtils
 
String sentence = "This is my < first caption 😄😃😀😊☺️😉😍😘😚😗😙😜😝😩😧👳😹👿😬🙊👄👃👀🙌👈👈💢👋🙆👔💚💄💄💓💖💪🙊💀👽🏃🙋💁👆👯💇👖👖🚝🗼🌅🎡⛲️🚔🚨⚠️🇬🇧🎪🚲🚲🚂🗼🏭🚗🚆🚅⛵️🐝🐔🐩🐕🐖🐁🌺🌺🌼🐇🐐🐐🌸"
 
String sentenceOut = ""
(0..<sentence.size()).each {
    if (Character.isHighSurrogate(sentence.charAt(it))) {
        sentenceOut += StringEscapeUtils.escapeHtml(sentence[it]+sentence[it+1])
        //sentenceOut += StringEscapeUtils.escapeHtml4(sentence[it]+sentence[it+1])
        println "escaping ${sentence[it]+sentence[it+1]}"
    } else if (Character.isLowSurrogate(sentence.charAt(it))){
    
    } else {
        sentenceOut += sentence[it]
    }
}
 
return sentenceOut