diff --git a/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/web/WebSessionOAuth2ReactiveAuthorizationRequestRepository.java b/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/web/WebSessionOAuth2ReactiveAuthorizationRequestRepository.java
index 2783c5968f..aa8b4302a6 100644
--- a/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/web/WebSessionOAuth2ReactiveAuthorizationRequestRepository.java
+++ b/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/web/WebSessionOAuth2ReactiveAuthorizationRequestRepository.java
@@ -84,7 +84,11 @@ public final class WebSessionOAuth2ReactiveAuthorizationRequestRepository implem
 				if (stateToAuthzRequest.isEmpty()) {
 					sessionAttrs.remove(this.sessionAttributeName);
 				}
-				sink.next(removedValue);
+				if (removedValue == null) {
+					sink.complete();
+				} else {
+					sink.next(removedValue);
+				}
 			});
 	}
 
diff --git a/oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/web/WebSessionOAuth2ReactiveAuthorizationRequestRepositoryTests.java b/oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/web/WebSessionOAuth2ReactiveAuthorizationRequestRepositoryTests.java
index c4fc7adaed..50d18bf6db 100644
--- a/oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/web/WebSessionOAuth2ReactiveAuthorizationRequestRepositoryTests.java
+++ b/oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/web/WebSessionOAuth2ReactiveAuthorizationRequestRepositoryTests.java
@@ -24,6 +24,7 @@ import org.junit.Test;
 import org.springframework.http.codec.ServerCodecConfigurer;
 import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
 import org.springframework.mock.http.server.reactive.MockServerHttpResponse;
+import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.mock.web.server.MockServerWebExchange;
 import org.springframework.security.oauth2.core.endpoint.OAuth2AuthorizationRequest;
 import org.springframework.security.oauth2.core.endpoint.OAuth2ParameterNames;
@@ -179,6 +180,23 @@ public class WebSessionOAuth2ReactiveAuthorizationRequestRepositoryTests {
 				.verifyComplete();
 	}
 
+	// gh-5599
+	@Test
+	public void removeAuthorizationRequestWhenStateMissingThenNoErrors() {
+		MockServerHttpRequest otherState = MockServerHttpRequest.get("/")
+				.queryParam(OAuth2ParameterNames.STATE, "other")
+				.build();
+		ServerWebExchange otherStateExchange = this.exchange.mutate()
+				.request(otherState)
+				.build();
+		Mono<OAuth2AuthorizationRequest> saveAndRemove = this.repository
+				.saveAuthorizationRequest(this.authorizationRequest, this.exchange)
+				.then(this.repository.removeAuthorizationRequest(otherStateExchange));
+
+		StepVerifier.create(saveAndRemove)
+				.verifyComplete();
+	}
+
 	@Test
 	public void removeAuthorizationRequestWhenMultipleThenOnlyOneRemoved() {
 		String oldState = "state0";