Fix potential race condition in Lazy.getNullable()

The getNullable() method had a subtle race condition where the value field
could be read as null after being assigned but before the resolved flag was
set to true. This could occur if another thread read the value between lines
136 and 137.

By using a local variable to store the supplier's result and returning that
directly, we ensure that the thread that computes the value will always
return the correct result, regardless of what other threads observe.

This change maintains the existing behavior documented in the class Javadoc
that the supplier may be called multiple times under concurrent access, while
fixing the potential for incorrect null returns.

Author: jbj338033

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

@@ -133,10 +133,11 @@ public T getNullable() {
 			return value;
 		}
 
-		this.value = supplier.get();
+		T result = supplier.get();
+		this.value = result;
 		this.resolved = true;
 
-		return value;
+		return result;
 	}
 
 	/**