Empty HAL-Forms options inline attribute should be serialized

Signed-off-by: Réda Housni Alaoui <reda-alaoui@hey.com>

Author: reda-alaoui

src/main/java/org/springframework/hateoas/mediatype/hal/forms/HalFormsOptions.java

@@ -309,6 +309,7 @@ private Inline(Collection<? extends Object> values, @Nullable String promptRef,
 		 * @return
 		 */
 		@JsonProperty
+		@JsonInclude(Include.ALWAYS)
 		public Collection<? extends Object> getInline() {
 			return inline;
 		}

src/test/java/org/springframework/hateoas/mediatype/hal/forms/HalFormsJacksonModuleIntegrationTest.java

@@ -481,6 +481,27 @@ void rendersFullInlineOptions() {
 				});
 	}
 
+	@Test // #2257
+	void rendersEmptyInlineOptions() {
+
+		var options = HalFormsOptions.inline()
+				.withPromptField("my-prompt-field")
+				.withValueField("my-value-field")
+				.withMinItems(2L)
+				.withMaxItems(3L);
+
+		getCuriedMapper()
+				.assertSerializes(options)
+				.into(result -> {
+
+					assertThat(result.read("$.inline", Collection.class)).isEmpty();
+					assertThat(result.read("$.promptField", String.class)).isEqualTo("my-prompt-field");
+					assertThat(result.read("$.valueField", String.class)).isEqualTo("my-value-field");
+					assertThat(result.read("$.minItems", Long.class)).isEqualTo(2L);
+					assertThat(result.read("$.maxItems", Long.class)).isEqualTo(3L);
+				});
+	}
+
 	@Test // #2257
 	void rendersFullRemoteOptions() {