logback-android/src/main/java/ch/qos/logback/core/subst/Parser.java
private Node Eopt() throws ScanException {
    Token next = peekAtCurentToken();
    if (next == null) {
      return null;
    } else {
      return E();
    }
  }
private Node Eopt() throws ScanException {
    Token next = peekAtCurentToken();
    if (next == null) {
      return null;
    } else {
      return E();
    }
  }
Eopt = E|~