Remove calling printStackTrace from BeanELResolver (https://github.com/zkoss/zk/blob/master/zel/src/org/zkoss/zel/BeanELResolver.java#L441) and (https://github.com/zkoss/zk/blob/master/zel/src/org/zkoss/zel/BeanELResolver.java#L454).

When an each is Map.Entry in this zul:
${each.key}: ${each.value}
This stack trace is printed:
java.lang.NoSuchMethodException: java.io.Serializable.getValue()
at java.lang.Class.getMethod(Class.java:1665)
at org.zkoss.zel.BeanELResolver.getMethod(BeanELResolver.java:434)
at org.zkoss.zel.BeanELResolver.getMethod(BeanELResolver.java:448)
at org.zkoss.zel.BeanELResolver.access$200(BeanELResolver.java:42)
at org.zkoss.zel.BeanELResolver$BeanProperty.read(BeanELResolver.java:401)
at org.zkoss.zel.BeanELResolver$BeanProperty.access$000(BeanELResolver.java:314)
at org.zkoss.zel.BeanELResolver.getValue(BeanELResolver.java:87)
at org.zkoss.zel.CompositeELResolver.getValue(CompositeELResolver.java:66)
at org.zkoss.xel.zel.XelELResolver.getValue(XelELResolver.java:72)