DATAMONGO-853 - Update does not allow null keys anymore.

Added check for blank / null keys when adding key to Update.

Original pull request: #129.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/query/Update.java

@@ -26,6 +26,7 @@ import java.util.Map;
 import java.util.Set;
 
 import org.springframework.dao.InvalidDataAccessApiUsageException;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 import com.mongodb.BasicDBObject;
@@ -263,12 +264,14 @@ public class Update {
 
 	protected void addFieldOperation(String operator, String key, Object value) {
 
+		Assert.hasText(key, "Key/Path for update must not be null or blank.");
 		modifierOps.put(operator, new BasicDBObject(key, value));
 		this.keysToUpdate.add(key);
 	}
 
 	protected void addMultiFieldOperation(String operator, String key, Object value) {
 
+		Assert.hasText(key, "Key/Path for update must not be null or blank.");
 		Object existingValue = this.modifierOps.get(operator);
 		DBObject keyValueMap;
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/query/UpdateTests.java

@@ -260,4 +260,28 @@ public class UpdateTests {
 
 		assertThat(clone.modifies("oof"), is(false));
 	}
+
+	/**
+	 * @see DATAMONGO-853
+	 */
+	@Test(expected = IllegalArgumentException.class)
+	public void testAddingMultiFieldOperationThrowsExceptionWhenCalledWithNullKey() {
+		new Update().addMultiFieldOperation("$op", null, "exprected to throw IllegalArgumentException.");
+	}
+
+	/**
+	 * @see DATAMONGO-853
+	 */
+	@Test(expected = IllegalArgumentException.class)
+	public void testAddingSingleFieldOperationThrowsExceptionWhenCalledWithNullKey() {
+		new Update().addFieldOperation("$op", null, "exprected to throw IllegalArgumentException.");
+	}
+
+	/**
+	 * @see DATAMONGO-853
+	 */
+	@Test(expected = IllegalArgumentException.class)
+	public void testCreatingUpdateWithNullKeyThrowsException() {
+		Update.update(null, "value");
+	}
 }