Two ッ characters cause StringIndexOutOfBoundsException

[phanecak-maptiler]

When transliterating "キッッズスクール加古川つばめ保育園" (name from https://www.openstreetmap.org/way/971134980) StringIndexOutOfBoundsException is thrown:

java.lang.StringIndexOutOfBoundsException: Index 0 out of bounds for length 0
        at java.base/jdk.internal.util.Preconditions$1.apply(Preconditions.java:55)
        at java.base/jdk.internal.util.Preconditions$1.apply(Preconditions.java:52)
        at java.base/jdk.internal.util.Preconditions$4.apply(Preconditions.java:213)
        at java.base/jdk.internal.util.Preconditions$4.apply(Preconditions.java:210)
        at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:98)
        at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:106)
        at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:302)
        at java.base/java.lang.String.checkIndex(String.java:4832)
        at java.base/java.lang.StringLatin1.charAt(StringLatin1.java:46)
        at java.base/java.lang.String.charAt(String.java:1555)
        at fr.free.nrw.jakaroma.Jakaroma.kuromojiFailedConvert(Jakaroma.java:172)
        at fr.free.nrw.jakaroma.Jakaroma.convert(Jakaroma.java:83)
        at ...