Remove usage of Assert.notNull(Object)

This commit updates the Spring Boot codebase to adapt to the removal of
`Assert.notNull(Object)` in SPR-15196.

See gh-8140

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/statsd/StatsdMetricWriter.java

@@ -72,7 +72,7 @@ public class StatsdMetricWriter implements MetricWriter, Closeable {
 	 * @param client StatsD client to write metrics with
 	 */
 	public StatsdMetricWriter(StatsDClient client) {
-		Assert.notNull(client);
+		Assert.notNull(client, "Client must not be null");
 		this.client = client;
 	}
 

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/ConditionalOnMissingBeanTests.java

@@ -580,7 +580,7 @@ public class ConditionalOnMissingBeanTests {
 	public static class ExampleFactoryBean implements FactoryBean<ExampleBean> {
 
 		public ExampleFactoryBean(String value) {
-			Assert.state(!value.contains("$"));
+			Assert.state(!value.contains("$"), "value should not contain '$'");
 		}
 
 		@Override
@@ -603,7 +603,7 @@ public class ConditionalOnMissingBeanTests {
 	public static class NonspecificFactoryBean implements FactoryBean<Object> {
 
 		public NonspecificFactoryBean(String value) {
-			Assert.state(!value.contains("$"));
+			Assert.state(!value.contains("$"), "value should not contain '$'");
 		}
 
 		@Override

spring-boot/src/main/java/org/springframework/boot/bind/PropertiesConfigurationFactory.java

@@ -89,7 +89,7 @@ public class PropertiesConfigurationFactory<T>
 	 * @see #PropertiesConfigurationFactory(Class)
 	 */
 	public PropertiesConfigurationFactory(T target) {
-		Assert.notNull(target);
+		Assert.notNull(target, "Target object must not be null");
 		this.target = target;
 	}
 
@@ -100,7 +100,7 @@ public class PropertiesConfigurationFactory<T>
 	 */
 	@SuppressWarnings("unchecked")
 	public PropertiesConfigurationFactory(Class<?> type) {
-		Assert.notNull(type);
+		Assert.notNull(type, "Target type must not be null");
 		this.target = (T) BeanUtils.instantiateClass(type);
 	}
 

spring-boot/src/main/java/org/springframework/boot/bind/YamlConfigurationFactory.java

@@ -73,7 +73,7 @@ public class YamlConfigurationFactory<T>
 	 * @param type the root type
 	 */
 	public YamlConfigurationFactory(Class<?> type) {
-		Assert.notNull(type);
+		Assert.notNull(type, "Root type must not be null");
 		this.type = type;
 	}