Fix handling of empty querty string parameters

Previously empty parameters in a query string were handled inconsistently such that they sometimes had a value of "" in a list and sometimes were represented as an empty list. This inconsistency lead to the parameter appearing twice in the cURL request snippet. This commit removes the inconsistency by always using an empty string to represent an empty query parameter value. Fixes gh-647

Author: wilkinsona

spring-restdocs-core/src/main/java/org/springframework/restdocs/operation/QueryStringParser.java

@@ -64,10 +64,8 @@ private void processParameter(String parameter, Parameters parameters) {
 parameters.add(decode(name), decode(value));
 }
 else {
-List<String> values = parameters.get(components[0]);
-if (values == null) {
-parameters.put(components[0], new LinkedList<String>());
-}
+List<String> values = parameters.computeIfAbsent(components[0], (p) -> new LinkedList<String>());
+values.add("");
 }
 }
 else {

spring-restdocs-core/src/test/java/org/springframework/restdocs/operation/QueryStringParserTests.java

@@ -81,4 +81,18 @@ public void malformedParameter() {
 this.queryStringParser.parse(URI.create("http://localhost?a=apple=avocado"));
 }
 
+@Test
+public void emptyParameter() {
+Parameters parameters = this.queryStringParser.parse(URI.create("http://localhost?a="));
+assertThat(parameters.size()).isEqualTo(1);
+assertThat(parameters).containsEntry("a", Arrays.asList(""));
+}
+
+@Test
+public void emptyAndNotEmptyParameter() {
+Parameters parameters = this.queryStringParser.parse(URI.create("http://localhost?a=&a=alpha"));
+assertThat(parameters.size()).isEqualTo(1);
+assertThat(parameters).containsEntry("a", Arrays.asList("", "alpha"));
+}
+
 }

spring-restdocs-mockmvc/src/test/java/org/springframework/restdocs/mockmvc/MockMvcRestDocumentationIntegrationTests.java

@@ -185,6 +185,19 @@ public void curlSnippetWithQueryStringOnPost() throws Exception {
 + " -H 'Accept: application/json' \\%n" + " -d 'a=alpha'"))));
 }
 
+@Test
+public void curlSnippetWithEmptyParameterQueryString() throws Exception {
+MockMvc mockMvc = MockMvcBuilders.webAppContextSetup(this.context)
+.apply(documentationConfiguration(this.restDocumentation)).build();
+mockMvc.perform(get("/").param("a", "").accept(MediaType.APPLICATION_JSON)).andExpect(status().isOk())
+.andDo(document("curl-snippet-with-empty-parameter-query-string"));
+assertThat(
+new File("build/generated-snippets/curl-snippet-with-empty-parameter-query-string/curl-request.adoc"))
+.has(content(codeBlock(TemplateFormats.asciidoctor(), "bash")
+.withContent(String.format("$ curl 'http://localhost:8080/?a=' -i -X GET \\%n"
++ " -H 'Accept: application/json'"))));
+}
+
 @Test
 public void curlSnippetWithContentAndParametersOnPost() throws Exception {
 MockMvc mockMvc = MockMvcBuilders.webAppContextSetup(this.context)

spring-restdocs-restassured/src/test/java/org/springframework/restdocs/restassured3/RestAssuredRestDocumentationIntegrationTests.java

@@ -120,6 +120,18 @@ public void curlSnippetWithCookies() throws Exception {
 + " -H 'Content-Type: " + contentType + "' \\%n" + " --cookie 'cookieName=cookieVal'"))));
 }
 
+@Test
+public void curlSnippetWithEmptyParameterQueryString() throws Exception {
+given().port(tomcat.getPort()).filter(documentationConfiguration(this.restDocumentation))
+.filter(document("curl-snippet-with-empty-parameter-query-string")).accept("application/json")
+.param("a", "").get("/").then().statusCode(200);
+assertThat(
+new File("build/generated-snippets/curl-snippet-with-empty-parameter-query-string/curl-request.adoc"))
+.has(content(codeBlock(TemplateFormats.asciidoctor(), "bash")
+.withContent(String.format("$ curl 'http://localhost:" + tomcat.getPort()
++ "/?a=' -i -X GET \\%n -H 'Accept: application/json'"))));
+}
+
 @Test
 public void curlSnippetWithQueryStringOnPost() throws Exception {
 given().port(tomcat.getPort()).filter(documentationConfiguration(this.restDocumentation))

spring-restdocs-webtestclient/src/test/java/org/springframework/restdocs/webtestclient/WebTestClientRestDocumentationIntegrationTests.java

@@ -165,6 +165,17 @@ public void curlSnippetWithCookies() throws Exception {
 + " -H 'Accept: application/json' \\%n" + " --cookie 'cookieName=cookieVal'"))));
 }
 
+@Test
+public void curlSnippetWithEmptyParameterQueryString() throws Exception {
+this.webTestClient.get().uri("/?a=").accept(MediaType.APPLICATION_JSON).exchange().expectStatus().isOk()
+.expectBody().consumeWith(document("curl-snippet-with-empty-parameter-query-string"));
+assertThat(
+new File("build/generated-snippets/curl-snippet-with-empty-parameter-query-string/curl-request.adoc"))
+.has(content(codeBlock(TemplateFormats.asciidoctor(), "bash")
+.withContent(String.format("$ curl 'https://api.example.com/?a=' -i -X GET \\%n"
++ " -H 'Accept: application/json'"))));
+}
+
 @Test
 public void httpieSnippetWithCookies() throws Exception {
 this.webTestClient.get().uri("/").cookie("cookieName", "cookieVal").accept(MediaType.APPLICATION_JSON)