presto-main/src/main/java/io/prestosql/metadata/BoundVariables.java/BoundVariables/containsValue
class BoundVariables:    private static boolean containsValue(Map<String, ?> map, String variableName)
    {
        checkState(variableName != null, "variableName is null");
        return map.containsKey(variableName);
    }