Backport bugfix and resolve conflicts.

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignClientFactoryBean.java

@@ -443,6 +443,9 @@ public class FeignClientFactoryBean
 	}
 
 	private String cleanPath() {
+		if (path == null) {
+			return "";
+		}
 		String path = this.path.trim();
 		if (StringUtils.hasLength(path)) {
 			if (!path.startsWith("/")) {

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignClientsRegistrar.java

@@ -302,7 +302,11 @@ class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLo
 			if (resolver == null) {
 				return resolved;
 			}
-			return String.valueOf(resolver.evaluate(resolved, new BeanExpressionContext(beanFactory, null)));
+			Object evaluateValue = resolver.evaluate(resolved, new BeanExpressionContext(beanFactory, null));
+			if (evaluateValue != null) {
+				return String.valueOf(evaluateValue);
+			}
+			return null;
 		}
 		return value;
 	}

spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/FeignClientsRegistrarTests.java

@@ -18,6 +18,7 @@ package org.springframework.cloud.openfeign;
 
 import java.util.Collections;
 
+import feign.Target;
 import org.junit.Test;
 
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
@@ -25,15 +26,19 @@ import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.mock.env.MockEnvironment;
+import org.springframework.test.util.ReflectionTestUtils;
 import org.springframework.web.bind.annotation.GetMapping;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 
 /**
  * @author Spencer Gibb
  * @author Gang Li
  * @author Michal Domagala
+ * @author Szymon Linowski
+ * @author Olga Maciaszek-Sharma
  */
 public class FeignClientsRegistrarTests {
 
@@ -101,6 +106,30 @@ public class FeignClientsRegistrarTests {
 				.doesNotThrowAnyException();
 	}
 
+	@Test
+	public void shouldResolveNullUrl() {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+		context.register(NullUrlFeignClientTestConfig.class);
+		context.refresh();
+
+		Object feignClientBean = context.getBean(NullUrlFeignClient.class);
+
+		Object invocationHandlerLambda = ReflectionTestUtils.getField(feignClientBean, "h");
+		Target.HardCodedTarget<NullUrlFeignClient> target = (Target.HardCodedTarget<NullUrlFeignClient>) ReflectionTestUtils
+				.getField(invocationHandlerLambda, "arg$4");
+		assertThat(target.name()).isEqualTo("nullUrlFeignClient");
+		assertThat(target.url()).isEqualTo("http://nullUrlFeignClient");
+	}
+
+	@Test
+	public void shouldResolveAndValidateNullName() {
+		assertThatIllegalStateException().isThrownBy(() -> {
+			AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+			context.register(NullExpressionNameFeignClientTestConfig.class);
+			context.refresh();
+		});
+	}
+
 	@FeignClient(name = "fallbackTestClient", url = "http://localhost:8080/", fallback = FallbackClient.class)
 	protected interface FallbackClient {
 
@@ -118,6 +147,16 @@ public class FeignClientsRegistrarTests {
 
 	}
 
+	@FeignClient(name = "nullUrlFeignClient", url = "${test.url:#{null}}", path = "${test.path:#{null}}")
+	protected interface NullUrlFeignClient {
+
+	}
+
+	@FeignClient(name = "${test.name:#{null}}")
+	protected interface NullExpressionNameFeignClient {
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@EnableAutoConfiguration
 	@EnableFeignClients(clients = { FeignClientsRegistrarTests.FallbackClient.class })
@@ -138,4 +177,18 @@ public class FeignClientsRegistrarTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	@EnableAutoConfiguration
+	@EnableFeignClients(clients = NullUrlFeignClient.class)
+	protected static class NullUrlFeignClientTestConfig {
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	@EnableAutoConfiguration
+	@EnableFeignClients(clients = NullExpressionNameFeignClient.class)
+	protected static class NullExpressionNameFeignClientTestConfig {
+
+	}
+
 }