Correct behavior for NSMutableData's replaceBytes(in:withBytes:length:) method for withBytes: nil case

Author: Frederick Kellison-Linn

Foundation/NSData.swift

@@ -942,12 +942,10 @@ open class NSMutableData : NSData {
         }
 
     }
-    
+
     open func replaceBytes(in range: NSRange, withBytes replacementBytes: UnsafeRawPointer?, length replacementLength: Int) {
-        if let replacementBytes = replacementBytes {
-            let bytePtr = replacementBytes.bindMemory(to: UInt8.self, capacity: replacementLength)
-            CFDataReplaceBytes(_cfMutableObject, CFRangeMake(range.location, range.length), bytePtr, replacementLength)
-        }
+        let bytePtr = replacementBytes?.bindMemory(to: UInt8.self, capacity: replacementLength)
+        CFDataReplaceBytes(_cfMutableObject, CFRangeMake(range.location, range.length), bytePtr, replacementLength)
     }
 }
 

TestFoundation/TestNSData.swift

@@ -421,8 +421,14 @@ class TestNSData: XCTestCase {
         let replacement = makeData([8, 9, 10])
         mData.replaceBytes(in: NSMakeRange(1, 3), withBytes: replacement.bytes,
             length: 3)
-        let expected = makeData([0, 8, 9, 10, 0])
+        var expected = makeData([0, 8, 9, 10, 0])
         XCTAssertEqual(mData, expected)
+
+        // test removing bytes with nil replacementBytes parameter
+        mData.replaceBytes(in: NSMakeRange(1, 3), withBytes: nil, length: 0)
+        expected = makeData([0, 0])
+        XCTAssertEqual(mData, expected)
+
     }
 
     func test_initDataWithCapacity() {