Add check for null value using hasValue; rename isNil to hasKey.

Squashed commit of the following:

commit dca6ef1
Merge: 3fe4c28 449f8ff
Author: Ben Kreeger <ben.kreeger@icloud.com>
Date:   Mon Oct 12 14:29:51 2015 -0500

    Merge branch 'feature/is-null' of github.com:kreeger/ModelRocket into feature/is-null

commit 3fe4c28
Author: Ben Kreeger <ben.kreeger@icloud.com>
Date:   Mon Oct 12 14:29:21 2015 -0500

    Alter new method to be hasValue, with isNil as hasKey, too.

commit 449f8ff
Author: Ben Kreeger <ben.kreeger@icloud.com>
Date:   Fri Oct 9 11:17:41 2015 -0500

    Change spaces to a tab.

commit 499dafd
Author: Ben Kreeger <ben.kreeger@icloud.com>
Date:   Fri Oct 9 11:13:50 2015 -0500

    Add ability to check for `null` in JSON with `is NSNull`.

Author: kreeger

ModelRocket/JSON.swift

@@ -70,9 +70,17 @@ public struct JSON {
         }
     }
 
-    public var isNil: Bool {
+    @available(*, deprecated=1.2, message="Use !hasKey instead.") public var isNil: Bool {
         return (object == nil)
     }
+    
+    public var hasKey: Bool {
+        return object != nil
+    }
+    
+    public var hasValue: Bool {
+        return !(object is NSNull)
+    }
 }
 
 // MARK: - CustomStringConvertible
@@ -285,6 +293,11 @@ extension Dictionary {
     }
 }
 
+// MARK: - NSNull
+
+extension JSON {
+}
+
 // MARK: - Equatable
 
 extension JSON: Equatable {}

ModelRocketTests/JSONTests.swift

@@ -55,7 +55,7 @@ class JSONTests: XCTestCase {
 
         // No data
         let emptyJSON = JSON(data: nil)
-        XCTAssertTrue(emptyJSON.isNil, "JSON not nil")
+        XCTAssertFalse(emptyJSON.hasKey, "JSON not nil")
 
         // String
         XCTAssertEqual(vehicleJSON["make"].stringValue, "BMW")
@@ -436,6 +436,16 @@ class JSONTests: XCTestCase {
         XCTAssertEqual(json["array"][0].intValue, 1)
     }
 
+    // MARK: - NSNull (from loaded data)
+    
+    func testNSNull() {
+        let jsonPath = NSBundle(forClass: self.dynamicType).pathForResource("Tests", ofType: "json")
+        let jsonData = NSData(contentsOfFile: jsonPath!)
+        let json = JSON(data: jsonData)
+        
+        XCTAssertFalse(json["driver"].hasValue)
+    }
+    
     // MARK: - Dictionary
 
     func testDictionaryLiteralConvertible() {

ModelRocketTests/Tests.json

@@ -6,6 +6,7 @@
 	"number_of_doors" : 4,
 	"zero_to_sixty_time" : 4.7,
 	"nav_system_standard" : true,
+	"driver": null,
 	"manufacturer" : {
 		"company_name" : "Bayerische Motoren Werke AG",
 		"headquarters" : "Munich, Bavaria, Germany",
@@ -22,4 +23,4 @@
     	"sedan" : 1024,
     	"gran_coupe" : 512
     }
-}
+}