diff --git a/build.gradle b/build.gradle
index d7cc862c82..6bbfdd891c 100644
--- a/build.gradle
+++ b/build.gradle
@@ -31,7 +31,7 @@ ext {
 	aspectjVersion       = "1.9.3"
 	coroutinesVersion    = "1.2.1"
 	freemarkerVersion    = "2.3.28"
-	groovyVersion        = "2.5.6"
+	groovyVersion        = "2.5.7"
 	hsqldbVersion        = "2.4.1"
 	jackson2Version      = "2.9.8"
 	jettyVersion         = "9.4.18.v20190429"
diff --git a/spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractBeanDefinition.java b/spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractBeanDefinition.java
index a845df267e..f05e0c0626 100644
--- a/spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractBeanDefinition.java
+++ b/spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractBeanDefinition.java
@@ -409,10 +409,13 @@ public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccess
 	}
 
 	/**
-	 * Return the class of the wrapped bean, if already resolved.
-	 * @return the bean class, or {@code null} if none defined
+	 * Return the class of the wrapped bean (assuming it is resolved already).
+	 * @return the bean class (never {@code null})
 	 * @throws IllegalStateException if the bean definition does not define a bean class,
-	 * or a specified bean class name has not been resolved into an actual Class
+	 * or a specified bean class name has not been resolved into an actual Class yet
+	 * @see #hasBeanClass()
+	 * @see #setBeanClass(Class)
+	 * @see #resolveBeanClass(ClassLoader)
 	 */
 	public Class<?> getBeanClass() throws IllegalStateException {
 		Object beanClassObject = this.beanClass;
@@ -428,6 +431,9 @@ public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccess
 
 	/**
 	 * Return whether this definition specifies a bean class.
+	 * @see #getBeanClass()
+	 * @see #setBeanClass(Class)
+	 * @see #resolveBeanClass(ClassLoader)
 	 */
 	public boolean hasBeanClass() {
 		return (this.beanClass instanceof Class);
diff --git a/spring-test/src/main/java/org/springframework/test/util/AssertionErrors.java b/spring-test/src/main/java/org/springframework/test/util/AssertionErrors.java
index aea7f8e4cf..1865847673 100644
--- a/spring-test/src/main/java/org/springframework/test/util/AssertionErrors.java
+++ b/spring-test/src/main/java/org/springframework/test/util/AssertionErrors.java
@@ -76,9 +76,9 @@ public abstract class AssertionErrors {
 	 * {@link AssertionError} otherwise.
 	 * @param message a message that describes the reason for the failure
 	 * @param object the object to check
-	 * @since 5.1
+	 * @since 5.1.8
 	 */
-	public static void assertNotNull(String message, Object object) {
+	public static void assertNotNull(String message, @Nullable Object object) {
 		assertTrue(message, object != null);
 	}