(Noted when reviewing org.apache.el.lang.ELSupport.coerceToType())

My expectations are that ELSupport.coerceToType() method follows the type conversion rules specified in Expression Language specification.

There is the following phrase in specification 3.0 ch.1.23.7 Coerce A to Any Other Type T:

"If A is a String and T's PropertyEditor throws an exception:"
"If A is "", return null"
"Otherwise, error"

The same phrase in present in EL 2.2 and EL 2.1 specifications (ch.1.18.7) as well.

Consider the following case:
- A is an empty string ("")
- T has a PropertyEditor

Expected behaviour:
- Call PropertyEditor with value of "".
- If it throws an exception, return null.
- Otherwise use the converted value.
try {
 propertyEditor.setAsText("").getValue();
} catch (RuntimeException e) {
 return null;
}

Actual implementation:
- It skips calling the PropertyEditor and immediately returns null.

 if (obj instanceof String) {
   if ("".equals(obj))
        return null;
   PropertyEditor editor = PropertyEditorManager.findEditor(type);
 ...

The PropertyEditor.setAsText(String) method is documented to throw IllegalArgumentException on invalid values. I think that EL API expects an ELException, so it is to be wrapped somewhere.