Support for static field access on non-public enums

Issue: SPR-16284

(cherry picked from commit 9beb978)

spring-beans/src/main/java/org/springframework/beans/TypeConverterDelegate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,6 +35,7 @@ import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.NumberUtils;
+import org.springframework.util.ReflectionUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -353,6 +354,7 @@ class TypeConverterDelegate {
 			// to be checked, hence we don't return it right away.
 			try {
 				Field enumField = requiredType.getField(trimmedValue);
+				ReflectionUtils.makeAccessible(enumField);
 				convertedValue = enumField.get(null);
 			}
 			catch (Throwable ex) {