diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AuthenticationStepsExecutor.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AuthenticationStepsExecutor.java
index 06ea54e62..3e6c0ca1c 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AuthenticationStepsExecutor.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AuthenticationStepsExecutor.java
@@ -92,6 +92,7 @@ public VaultToken login() throws VaultException {
 				String.format("Cannot retrieve VaultToken from authentication chain. Got instead %s", state));
 	}
 
+	@SuppressWarnings({ "unchecked", "ConstantConditions" })
 	private Object evaluate(Iterable<Node<?>> steps) {
 
 		Object state = null;
@@ -144,28 +145,6 @@ private Object evaluate(Iterable<Node<?>> steps) {
 		return state;
 	}
 
-	private static Object doScalarValueStep(ScalarValueStep<Object> scalarValueStep) {
-		return scalarValueStep.get();
-	}
-
-	private static Object doSupplierStep(SupplierStep<Object> supplierStep) {
-		return supplierStep.get();
-	}
-
-	private static Object doMapStep(MapStep<Object, Object> o, Object state) {
-		return o.apply(state);
-	}
-
-	private Object doZipStep(ZipStep<Object, Object> o, Object state) {
-
-		Object result = evaluate(o.getRight());
-		return Pair.of(state, result);
-	}
-
-	private static Object doOnNext(OnNextStep<Object> o, Object state) {
-		return o.apply(state);
-	}
-
 	@SuppressWarnings("ConstantConditions")
 	@Nullable
 	private Object doHttpRequest(HttpRequestNode<Object> step, @Nullable Object state) {
@@ -187,7 +166,7 @@ private Object doHttpRequest(HttpRequestNode<Object> step, @Nullable Object stat
 
 	}
 
-	private static HttpEntity<?> getEntity(HttpEntity<?> entity, @Nullable Object state) {
+	private static HttpEntity<?> getEntity(@Nullable HttpEntity<?> entity, @Nullable Object state) {
 
 		if (entity == null) {
 			return state == null ? HttpEntity.EMPTY : new HttpEntity<>(state);
@@ -200,4 +179,26 @@ private static HttpEntity<?> getEntity(HttpEntity<?> entity, @Nullable Object st
 		return entity;
 	}
 
+	private static Object doMapStep(MapStep<Object, Object> o, Object state) {
+		return o.apply(state);
+	}
+
+	private Object doZipStep(ZipStep<Object, Object> o, Object state) {
+
+		Object result = evaluate(o.getRight());
+		return Pair.of(state, result);
+	}
+
+	private static Object doOnNext(OnNextStep<Object> o, Object state) {
+		return o.apply(state);
+	}
+
+	private static Object doScalarValueStep(ScalarValueStep<Object> scalarValueStep) {
+		return scalarValueStep.get();
+	}
+
+	private static Object doSupplierStep(SupplierStep<Object> supplierStep) {
+		return supplierStep.get();
+	}
+
 }
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AuthenticationStepsOperator.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AuthenticationStepsOperator.java
index 64f2737c8..8416e3262 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AuthenticationStepsOperator.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AuthenticationStepsOperator.java
@@ -29,6 +29,7 @@
 import org.springframework.core.io.buffer.DataBufferUtils;
 import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.http.HttpEntity;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.vault.VaultException;
 import org.springframework.vault.authentication.AuthenticationSteps.HttpRequest;
@@ -117,7 +118,7 @@ public Mono<VaultToken> getVaultToken() throws VaultException {
 	@SuppressWarnings("unchecked")
 	private Mono<Object> createMono(Iterable<Node<?>> steps) {
 
-		Mono<Object> state = Mono.just(Undefinded.INSTANCE);
+		Mono<Object> state = Mono.just(Undefinded.UNDEFINDED);
 
 		for (Node<?> o : steps) {
 
@@ -157,43 +158,6 @@ private Mono<Object> createMono(Iterable<Node<?>> steps) {
 		return state;
 	}
 
-	private static Object doScalarValueStep(ScalarValueStep<Object> scalarValueStep) {
-		return scalarValueStep.get();
-	}
-
-	private Mono<Object> doSupplierStepLater(SupplierStep<Object> supplierStep) {
-
-		Supplier<?> supplier = supplierStep.getSupplier();
-
-		if (!(supplier instanceof ResourceCredentialSupplier)) {
-			return Mono.fromSupplier(supplierStep.getSupplier()).subscribeOn(Schedulers.boundedElastic());
-		}
-
-		ResourceCredentialSupplier resourceSupplier = (ResourceCredentialSupplier) supplier;
-
-		return DataBufferUtils.join(DataBufferUtils.read(resourceSupplier.getResource(), this.factory, 4096))
-				.map(dataBuffer -> {
-					String result = dataBuffer.toString(ResourceCredentialSupplier.CHARSET);
-					DataBufferUtils.release(dataBuffer);
-					return (Object) result;
-				}).onErrorMap(IOException.class,
-						e -> new VaultException(
-								String.format("Credential retrieval from %s failed", resourceSupplier.getResource()),
-								e));
-	}
-
-	private static Object doMapStep(MapStep<Object, Object> o, Object state) {
-		return o.apply(state);
-	}
-
-	private Mono<Object> doZipStep(ZipStep<Object, Object> o) {
-		return createMono(o.getRight());
-	}
-
-	private static Object doOnNext(OnNextStep<Object> o, Object state) {
-		return o.apply(state);
-	}
-
 	private Mono<Object> doHttpRequest(HttpRequestNode<Object> step, Object state) {
 
 		HttpRequest<Object> definition = step.getDefinition();
@@ -213,14 +177,14 @@ private Mono<Object> doHttpRequest(HttpRequestNode<Object> step, Object state) {
 			spec = spec.header(header.getKey(), header.getValue().get(0));
 		}
 
-		if (entity.getBody() != null && !entity.getBody().equals(Undefinded.INSTANCE)) {
+		if (entity.getBody() != null && !entity.getBody().equals(Undefinded.UNDEFINDED)) {
 			return spec.bodyValue(entity.getBody()).retrieve().bodyToMono(definition.getResponseType());
 		}
 
 		return spec.retrieve().bodyToMono(definition.getResponseType());
 	}
 
-	private static HttpEntity<?> getEntity(HttpEntity<?> entity, Object state) {
+	private static HttpEntity<?> getEntity(@Nullable HttpEntity<?> entity, @Nullable Object state) {
 
 		if (entity == null) {
 			return state == null ? HttpEntity.EMPTY : new HttpEntity<>(state);
@@ -233,13 +197,47 @@ private static HttpEntity<?> getEntity(HttpEntity<?> entity, Object state) {
 		return entity;
 	}
 
-	static class Undefinded {
+	private static Object doMapStep(MapStep<Object, Object> o, Object state) {
+		return o.apply(state);
+	}
 
-		static final Undefinded INSTANCE = new Undefinded();
+	private Mono<Object> doZipStep(ZipStep<Object, Object> o) {
+		return createMono(o.getRight());
+	}
+
+	private static void doOnNext(OnNextStep<Object> o, Object state) {
+		o.apply(state);
+	}
+
+	private static Object doScalarValueStep(ScalarValueStep<Object> scalarValueStep) {
+		return scalarValueStep.get();
+	}
+
+	private Mono<Object> doSupplierStepLater(SupplierStep<Object> supplierStep) {
+
+		Supplier<?> supplier = supplierStep.getSupplier();
 
-		private Undefinded() {
+		if (!(supplier instanceof ResourceCredentialSupplier)) {
+			return Mono.fromSupplier(supplierStep.getSupplier()).subscribeOn(Schedulers.boundedElastic());
 		}
 
+		ResourceCredentialSupplier resourceSupplier = (ResourceCredentialSupplier) supplier;
+
+		return DataBufferUtils.join(DataBufferUtils.read(resourceSupplier.getResource(), this.factory, 4096))
+				.map(dataBuffer -> {
+					String result = dataBuffer.toString(ResourceCredentialSupplier.CHARSET);
+					DataBufferUtils.release(dataBuffer);
+					return (Object) result;
+				}).onErrorMap(IOException.class,
+						e -> new VaultException(
+								String.format("Credential retrieval from %s failed", resourceSupplier.getResource()),
+								e));
+	}
+
+	enum Undefinded {
+
+		UNDEFINDED;
+
 	}
 
 }