Use AssertJ's isEmpty() instead of hasSize(0)

Achieved via global search-and-replace.

spring-web/src/test/java/org/springframework/http/HttpHeadersTests.java

@@ -619,9 +619,9 @@ public class HttpHeadersTests {
 		// clear()
 		keySet.clear();
 		assertThat(keySet.isEmpty()).isTrue();
-		assertThat(keySet).hasSize(0);
+		assertThat(keySet).isEmpty();
 		assertThat(headers.isEmpty()).isTrue();
-		assertThat(headers).hasSize(0);
+		assertThat(headers).isEmpty();
 
 		// Unsupported operations
 		assertThatExceptionOfType(UnsupportedOperationException.class)

spring-web/src/test/java/org/springframework/http/server/ServletServerHttpRequestTests.java

@@ -155,7 +155,7 @@ public class ServletServerHttpRequestTests {
 	void getHeadersWithWildcardContentType() {
 		mockRequest.setContentType("*/*");
 		mockRequest.removeHeader("Content-Type");
-		assertThat(request.getHeaders()).as("Invalid content-type should not raise exception").hasSize(0);
+		assertThat(request.getHeaders()).as("Invalid content-type should not raise exception").isEmpty();
 	}
 
 	@Test

spring-web/src/test/java/org/springframework/http/server/reactive/ChannelSendOperatorTests.java

@@ -66,7 +66,7 @@ class ChannelSendOperatorTests {
 		assertThat(signal).isNotNull();
 		assertThat(signal.isOnComplete()).as("Unexpected signal: " + signal).isTrue();
 
-		assertThat(this.writer.items).hasSize(0);
+		assertThat(this.writer.items).isEmpty();
 		assertThat(this.writer.completed).isTrue();
 	}
 

spring-web/src/test/java/org/springframework/http/server/reactive/HeadersAdaptersTests.java

@@ -110,7 +110,7 @@ class HeadersAdaptersTests {
 		headers.add("TestHeader", "first");
 		assertThat(headers.keySet()).hasSize(1);
 		headers.keySet().removeIf("TestHeader"::equals);
-		assertThat(headers.keySet()).hasSize(0);
+		assertThat(headers.keySet()).isEmpty();
 	}
 
 	@ParameterizedHeadersTest

spring-web/src/test/java/org/springframework/http/server/reactive/ServerHttpRequestTests.java

@@ -53,7 +53,7 @@ public class ServerHttpRequestTests {
 	@Test
 	public void queryParamsNone() throws Exception {
 		MultiValueMap<String, String> params = createRequest("/path").getQueryParams();
-		assertThat(params).hasSize(0);
+		assertThat(params).isEmpty();
 	}
 
 	@Test

spring-web/src/test/java/org/springframework/web/util/WebUtilsTests.java

@@ -63,7 +63,7 @@ public class WebUtilsTests {
 		MultiValueMap<String, String> variables;
 
 		variables = WebUtils.parseMatrixVariables(null);
-		assertThat(variables).hasSize(0);
+		assertThat(variables).isEmpty();
 
 		variables = WebUtils.parseMatrixVariables("year");
 		assertThat(variables).hasSize(1);

spring-web/src/test/java/org/springframework/web/util/pattern/PathPatternTests.java

@@ -577,7 +577,7 @@ public class PathPatternTests {
 		pri = getPathRemaining(pp, "/aaa/bbb");
 		assertThat(pri.getPathRemaining().value()).isEqualTo("");
 		assertThat(pri.getPathMatched().value()).isEqualTo("/aaa/bbb");
-		assertThat(pri.getUriVariables()).hasSize(0);
+		assertThat(pri.getUriVariables()).isEmpty();
 
 		pp = parse("/*/{foo}/b*");
 		pri = getPathRemaining(pp, "/foo");
@@ -807,7 +807,7 @@ public class PathPatternTests {
 		assertThat((Object) checkCapture("/{one}/", "//")).isNull();
 		assertThat((Object) checkCapture("", "/abc")).isNull();
 
-		assertThat(checkCapture("", "").getUriVariables()).hasSize(0);
+		assertThat(checkCapture("", "").getUriVariables()).isEmpty();
 		checkCapture("{id}", "99", "id", "99");
 		checkCapture("/customer/{customerId}", "/customer/78", "customerId", "78");
 		checkCapture("/customer/{customerId}/banana", "/customer/42/banana", "customerId",
@@ -817,7 +817,7 @@ public class PathPatternTests {
 				"apple");
 		checkCapture("/{bla}.*", "/testing.html", "bla", "testing");
 		PathPattern.PathMatchInfo extracted = checkCapture("/abc", "/abc");
-		assertThat(extracted.getUriVariables()).hasSize(0);
+		assertThat(extracted.getUriVariables()).isEmpty();
 		checkCapture("/{bla}/foo","/a/foo");
 	}