Handle null value in OnExpressionCondition

Closes gh-2886

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/OnExpressionCondition.java

@@ -51,8 +51,9 @@ class OnExpressionCondition extends SpringBootCondition {
 		if (resolver == null) {
 			resolver = new StandardBeanExpressionResolver();
 		}
-		boolean result = (Boolean) resolver.evaluate(expression, expressionContext);
-		return new ConditionOutcome(result, ConditionMessage
+		Object result = resolver.evaluate(expression, expressionContext);
+		boolean match = result == null ? false : (boolean) result;
+		return new ConditionOutcome(match, ConditionMessage
 				.forCondition(ConditionalOnExpression.class, "(" + rawExpression + ")")
 				.resultedIn(result));
 	}

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

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2012-2017 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.condition;
+
+import java.util.Collections;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
+
+import org.springframework.beans.factory.config.BeanExpressionResolver;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.context.annotation.ConditionContext;
+import org.springframework.core.env.Environment;
+import org.springframework.core.type.AnnotatedTypeMetadata;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.BDDMockito.when;
+
+/**
+ * Tests for the {@link OnExpressionCondition}.
+ *
+ * @author Kristine Jetzke
+ */
+@RunWith(MockitoJUnitRunner.class)
+public class OnExpressionConditionTest {
+
+	@Mock
+	private ConditionContext context;
+
+	@Mock
+	private AnnotatedTypeMetadata metadata;
+
+	@Mock
+	private Environment environment;
+
+	@Mock
+	private ConfigurableListableBeanFactory beanFactory;
+
+	@Mock
+	private BeanExpressionResolver resolver;
+
+	@Before
+	public void setup() {
+		when(this.context.getEnvironment()).thenReturn(this.environment);
+		when(this.environment.resolvePlaceholders(any())).thenReturn("foo");
+		when(this.context.getBeanFactory()).thenReturn(this.beanFactory);
+		when(this.beanFactory.getBeanExpressionResolver()).thenReturn(this.resolver);
+
+		when(this.metadata.getAnnotationAttributes(any()))
+				.thenReturn(Collections.singletonMap("value", "bar"));
+	}
+
+	@Test
+	public void nullShouldEvaluateToFalse() {
+		when(this.resolver.evaluate(any(), any())).thenReturn(null);
+
+		OnExpressionCondition condition = new OnExpressionCondition();
+		ConditionOutcome conditionOutcome = condition.getMatchOutcome(this.context,
+				this.metadata);
+
+		assertThat(conditionOutcome.isMatch()).isFalse();
+	}
+
+}