Allow optional request body

core/src/main/java/feign/MethodMetadata.java

@@ -44,6 +44,7 @@ public final class MethodMetadata implements Serializable {
   private transient Map<Integer, Expander> indexToExpander;
   private BitSet parameterToIgnore = new BitSet();
   private boolean ignored;
+  private boolean bodyRequired = true;
   private transient Class<?> targetType;
   private transient Method method;
   private final transient List<String> warnings = new ArrayList<>();
@@ -228,6 +229,14 @@ public boolean isIgnored() {
     return ignored;
   }
 
+  public boolean isBodyRequired() {
+    return bodyRequired;
+  }
+
+  public void setBodyRequired(boolean bodyRequired) {
+    this.bodyRequired = bodyRequired;
+  }
+
   @Experimental
   public MethodMetadata targetType(Class<?> targetType) {
     this.targetType = targetType;

core/src/main/java/feign/RequestTemplateFactoryResolver.java

@@ -261,7 +261,9 @@ protected RequestTemplate resolve(
       Object body = null;
       if (!alwaysEncodeBody) {
         body = argv[metadata.bodyIndex()];
-        checkArgument(body != null, "Body parameter %s was null", metadata.bodyIndex());
+        if (mutable.methodMetadata().isBodyRequired()) {
+          checkArgument(body != null, "Body parameter %s was null", metadata.bodyIndex());
+        }
       }
 
       try {

spring/src/main/java/feign/spring/SpringContract.java

@@ -116,6 +116,7 @@ public SpringContract() {
     registerParameterAnnotation(
         RequestBody.class,
         (body, data, paramIndex) -> {
+          data.setBodyRequired(body.required());
           handleConsumesAnnotation(data, "application/json");
         });
     registerParameterAnnotation(RequestParam.class, requestParamParameterAnnotationProcessor());

spring/src/test/java/feign/spring/SpringContractTest.java

@@ -76,6 +76,8 @@ void setup() throws IOException {
             .noContent(HttpMethod.GET, "/health/optional")
             .noContent(HttpMethod.GET, "/health/optional?param=value")
             .noContent(HttpMethod.GET, "/health/optional?param")
+            .noContent(HttpMethod.POST, "/health/withNonRequiredRequestBody")
+            .noContent(HttpMethod.POST, "/health/withRequiredRequestBody")
             .noContent(HttpMethod.GET, "/health/1?deep=true")
             .noContent(HttpMethod.GET, "/health/1?deep=true&dryRun=true")
             .noContent(HttpMethod.GET, "/health/name?deep=true&dryRun=true")
@@ -166,6 +168,32 @@ void optionalNullable() {
     mockClient.verifyOne(HttpMethod.GET, "/health/optional");
   }
 
+  @Test
+  void requiredRequestBodyIsNull() {
+    Throwable exception =
+        assertThrows(
+            IllegalArgumentException.class, () -> resource.checkWithRequiredRequestBody(null));
+    assertThat(exception.getMessage()).contains("Body parameter 0 was null");
+  }
+
+  @Test
+  void nonRequiredRequestBodyIsNull() {
+    resource.checkWithNonRequiredRequestBody(null);
+
+    Request request = mockClient.verifyOne(HttpMethod.POST, "/health/withNonRequiredRequestBody");
+    assertThat(request.requestTemplate().body()).asString().isEqualTo("null");
+  }
+
+  @Test
+  void nonRequiredRequestBodyIsObject() {
+    UserObject object = new UserObject();
+    object.setName("hello");
+    resource.checkWithNonRequiredRequestBody(object);
+
+    Request request = mockClient.verifyOne(HttpMethod.POST, "/health/withNonRequiredRequestBody");
+    assertThat(request.requestTemplate().body()).asString().contains("\"name\" : \"hello\"");
+  }
+
   @Test
   void requestPart() {
     resource.checkRequestPart("1", "hello", "6");
@@ -302,6 +330,12 @@ void checkWithName(
     @RequestMapping(value = "/optional", method = RequestMethod.GET)
     void checkWithOptional(@RequestParam(name = "param") Optional<String> param);
 
+    @RequestMapping(value = "/withNonRequiredRequestBody", method = RequestMethod.POST)
+    void checkWithNonRequiredRequestBody(@RequestBody(required = false) UserObject obj);
+
+    @RequestMapping(value = "/withRequiredRequestBody", method = RequestMethod.POST)
+    void checkWithRequiredRequestBody(@RequestBody() UserObject obj);
+
     @RequestMapping(value = "/part/{id}", method = RequestMethod.POST)
     void checkRequestPart(
         @PathVariable(name = "id") String campaignId,
@@ -319,6 +353,19 @@ void checkRequestHeader(
     void checkRequestHeaderPojo(@RequestHeader HeaderMapUserObject object);
   }
 
+  class UserObject {
+    @Param("name1")
+    private String name;
+
+    public String getName() {
+      return name;
+    }
+
+    public void setName(String name) {
+      this.name = name;
+    }
+  }
+
   class HeaderMapUserObject {
     @Param("name1")
     private String name;