@Override
		public boolean canWrite(EvaluationContext context, Object target, String name) throws AccessException {
			throw new UnsupportedOperationException("Should not be called on an MessageOptimalPropertyAccessor");
		}
A {@link PropertyAccessor} reading values from a backing {@link Message} used by a
partition key. In a way this is similar than {@link MapAccessor} for header but also
adds 'payload' and 'headers' to be resolved. Having 'payload' or 'headers' keywords
in headers is not possible to access via this accessor.

@author Janne Valkealahti
spring-xd-hadoop/src/main/java/org/springframework/xd/integration/hadoop/expression/MessagePartitionKeyPropertyAccessor.java