--- a/src/java.base/share/classes/java/time/ZoneId.java	Thu Dec 13 16:14:07 2018 +0100
+++ b/src/java.base/share/classes/java/time/ZoneId.java	Thu Dec 13 15:31:05 2018 +0100
@@ -372,7 +372,7 @@
     public static ZoneId ofOffset(String prefix, ZoneOffset offset) {
         Objects.requireNonNull(prefix, "prefix");
         Objects.requireNonNull(offset, "offset");
-        if (prefix.length() == 0) {
+        if (prefix.isEmpty()) {
             return offset;
         }