Polishing.

Reduce TypeDiscoverer.isNullableWrapper method visibility to private to avoid exposure in preparation for wider value type support.

Original pull request: #2394.
See #2390.

src/main/java/org/springframework/data/util/TypeDiscoverer.java

@@ -25,7 +25,16 @@ import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.lang.reflect.TypeVariable;
 import java.lang.reflect.WildcardType;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Collectors;
 
@@ -309,6 +318,8 @@ class TypeDiscoverer<S> implements TypeInformation<S> {
 			return getComponentType();
 		}
 
+		// TODO: Consider that we will support value types beyond Optional<T>, such as Json<T>, Foo<T> that should remain
+		// configurable.
 		if (isNullableWrapper()) {
 			return getComponentType();
 		}
@@ -529,6 +540,10 @@ class TypeDiscoverer<S> implements TypeInformation<S> {
 		throw new IllegalArgumentException(String.format("Type %s not contained in candidates %s!", type, candidates));
 	}
 
+	private boolean isNullableWrapper() {
+		return NullableWrapperConverters.supports(getType());
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Object#equals(java.lang.Object)

src/main/java/org/springframework/data/util/TypeInformation.java

@@ -274,13 +274,4 @@ public interface TypeInformation<S> {
 		return !type.equals(getType()) && type.isAssignableFrom(getType());
 	}
 
-	/**
-	 * Returns whether the current type is considered a {@literal null} value wrapper or not.
-	 *
-	 * @return {@literal true} if the type is considered to be a {@literal null} value wrapper such as {@link java.util.Optional}.
-	 */
-	default boolean isNullableWrapper() {
-		return NullableWrapperConverters.supports(getType());
-	}
-
 }