code: @Override
  	public boolean isReadOnly(ELContext context, Object base, Object property) {
  		if (context == null) {
  			throw new NullPointerException("context is null");
  		}
  		if (isResolvable(base)) {
  			toIndex((List<?>) base, property);
  			context.setPropertyResolved(true);
  		}
  		return readOnly;
  	}
docs: If the base object is a list, returns whether a call to
  {@link #setValue(ELContext, Object, Object, Object)} will always fail. If the base is a List,
  the propertyResolved property of the ELContext object must be set to true by this resolver,
  before returning. If this property is not true after this method is called, the caller should
  ignore the return value. If this resolver was constructed in read-only mode, this method will
  always return true. If a List was created using java.util.Collections.unmodifiableList(List),
  this method must return true. Unfortunately, there is no Collections API method to detect
  this. However, an implementation can create a prototype unmodifiable List and query its
  runtime type to see if it matches the runtime type of the base object as a workaround.
  
  @param context
  The context of this evaluation.
  @param base
  The list to analyze. Only bases of type List are handled by this resolver.
  @param property
  The index of the element in the list to return the acceptable type for. Will be
  coerced into an integer, but otherwise ignored by this resolver.
  @return If the propertyResolved property of ELContext was set to true, then true if calling
  the setValue method will always fail or false if it is possible that such a call may
  succeed; otherwise undefined.
  @throws PropertyNotFoundException
  if the given index is out of bounds for this list.
  @throws IllegalArgumentException
  if the property could not be coerced into an integer.
  @throws NullPointerException
  if context is null
  @throws ELException
  if an exception was thrown while performing the property or variable resolution.
  The thrown exception must be included as the cause property of this exception, if
  available.