fix exists/not_exists helpers

src/main/java/org/cobbzilla/util/handlebars/HandlebarsUtil.java

@@ -16,7 +16,6 @@ import lombok.Getter;
 import lombok.Setter;
 import lombok.extern.slf4j.Slf4j;
 import org.apache.commons.collections.iterators.ArrayIterator;
-import org.apache.commons.collections4.map.SingletonMap;
 import org.apache.commons.lang3.RandomStringUtils;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.pdfbox.io.IOUtils;