Return null on absent Policy via VaultSysTemplate.getPolicy(…).

We now return null if a policy was not found. Previously, a VaultException was thrown.

Closes gh-202.

spring-vault-core/src/main/java/org/springframework/vault/core/VaultSysTemplate.java

@@ -216,11 +216,19 @@ public class VaultSysTemplate implements VaultSysOperations {
 
 		return vaultOperations.doWithSession(restOperations -> {
 
-			ResponseEntity<VaultResponse> response = restOperations.getForEntity(
-					"sys/policy/{name}", VaultResponse.class, name);
+			ResponseEntity<VaultResponse> response;
 
-			if (response.getStatusCode() == HttpStatus.NOT_FOUND) {
-				return null;
+			try {
+				response = restOperations.getForEntity("sys/policy/{name}",
+						VaultResponse.class, name);
+			}
+			catch (HttpStatusCodeException e) {
+
+				if (e.getStatusCode() == HttpStatus.NOT_FOUND) {
+					return null;
+				}
+
+				throw e;
 			}
 
 			String rules = (String) response.getBody().getRequiredData().get("rules");

spring-vault-core/src/test/java/org/springframework/vault/core/VaultSysTemplateIntegrationTests.java

@@ -153,6 +153,16 @@ public class VaultSysTemplateIntegrationTests extends IntegrationTestSupport {
 		assertThat(root).isEqualTo(Policy.empty());
 	}
 
+	@Test
+	public void shouldReadAbsentRootPolicy() {
+
+		assumeTrue(vaultVersion.isGreaterThanOrEqualTo(Version.parse("0.6.1")));
+
+		Policy root = adminOperations.getPolicy("absent-policy");
+
+		assertThat(root).isNull();
+	}
+
 	@Test(expected = UnsupportedOperationException.class)
 	public void shouldReadDefaultPolicy() {