diff --git a/core/src/main/java/io/parsingdata/metal/expression/value/reference/Ref.java b/core/src/main/java/io/parsingdata/metal/expression/value/reference/Ref.java
index f874b94a..91775e4b 100644
--- a/core/src/main/java/io/parsingdata/metal/expression/value/reference/Ref.java
+++ b/core/src/main/java/io/parsingdata/metal/expression/value/reference/Ref.java
@@ -24,7 +24,6 @@
 import static io.parsingdata.metal.expression.value.NotAValue.NOT_A_VALUE;
 
 import java.util.Objects;
-import java.util.Optional;
 import java.util.function.Predicate;
 
 import io.parsingdata.metal.Trampoline;