DATACOUCH-604 - Fix NPE when looking for Id field in interface.

This was failing with a repository for the domain object CouchbaseOAuth2AccessToken.
The following dependency is needed.

        <dependency>
            <groupId>org.springframework.security.oauth</groupId>
            <artifactId>spring-security-oauth2</artifactId>
            <version>2.4.1.RELEASE</version>
        </dependency>

package org.springframework.data.couchbase.domain;

import org.springframework.data.annotation.Id;
import org.springframework.data.couchbase.core.mapping.Document;
import org.springframework.data.couchbase.core.mapping.Field;
import org.springframework.security.oauth2.common.DefaultOAuth2AccessToken;
import org.springframework.security.oauth2.common.OAuth2AccessToken;

@Document(expiry = 30 * 24 * 60 * 60)
public class CouchbaseOAuth2AccessToken extends DefaultOAuth2AccessToken {

	private static final long serialVersionUID = 6537949925775752989L;

	@Id
	private String tokenId;

	@Field
	private String authentication;

	@Field
	private String authenticationKey;

	@Field
	private String clientId;

	@Field
	private String userName;

	// getters and setters omitted for brevity

	private CouchbaseOAuth2AccessToken() {
		this((String) null);
	}

	public CouchbaseOAuth2AccessToken(OAuth2AccessToken accessToken) {
		super(accessToken);
		this.tokenId = accessToken.getValue();
	}

	public CouchbaseOAuth2AccessToken(String value) {
		super(value);
		this.tokenId = value;
	}

}

src/main/java/org/springframework/data/couchbase/core/mapping/BasicCouchbasePersistentProperty.java

@@ -16,7 +16,6 @@
 
 package org.springframework.data.couchbase.core.mapping;
 
-import org.springframework.data.annotation.Id;
 import org.springframework.data.mapping.Association;
 import org.springframework.data.mapping.MappingException;
 import org.springframework.data.mapping.model.AnnotationBasedPersistentProperty;
@@ -28,8 +27,6 @@ import org.springframework.util.StringUtils;
 
 import com.couchbase.client.core.deps.com.fasterxml.jackson.annotation.JsonProperty;
 
-import java.util.Locale;
-
 /**
  * Implements annotated property representations of a given {@link Field} instance.
  * <p/>
@@ -99,7 +96,13 @@ public class BasicCouchbasePersistentProperty extends AnnotationBasedPersistentP
 	// DATACOUCH-145: allows SDK's @Id annotation to be used
 	@Override
 	public boolean isIdProperty() {
-		return isAnnotationPresent(Id.class) || super.isIdProperty()
-				|| this.getFieldName().toLowerCase(Locale.ROOT).equals("id");
+		if (super.isIdProperty()){
+			return true;
+		}
+		// is field named "id"
+		if(getName().equals("id")){
+			return true;
+		}
+		return false;
 	}
 }