Invalid Java enum declaration shown as good code in Intellij IDEA

State.java

package test;

import java.util.Collection;
import java.util.Collections;

import static java.util.Arrays.asList;
import static java.util.Collections.unmodifiableCollection;

public enum State {
    STATE1 {
        private Collection<State> accessibleFrom = unmodifiableCollection( asList( STATE2 ) );

        @Override
        public Collection<State> accessibleFrom() {
            return accessibleFrom;
        }
    },
    STATE2 {
        private Collection<State> accessibleFrom = unmodifiableCollection( asList( STATE1, STATE3 ) );

        @Override
        public Collection<State> accessibleFrom() {
            return accessibleFrom;
        }
    },
    STATE3 {
        private Collection<State> accessibleFrom = Collections.emptyList();

        @Override
        public Collection<State> accessibleFrom() {
            return accessibleFrom;
        }
    };

    public abstract Collection<State> accessibleFrom();

    public boolean accessibleFrom( State state ) {
        return state == this || accessibleFrom().contains( state );
    }
}