support especial keypath (such as ".ext" "a...b") in some situation: #112

YYModel/NSObject+YYModel.m

@@ -546,6 +546,14 @@ static force_inline id YYValueForMultiKeys(__unsafe_unretained NSDictionary *dic
                 
                 propertyMeta->_mappedToKey = mappedToKey;
                 NSArray *keyPath = [mappedToKey componentsSeparatedByString:@"."];
+                for (NSString *onePath in keyPath) {
+                    if (onePath.length == 0) {
+                        NSMutableArray *tmp = keyPath.mutableCopy;
+                        [tmp removeObject:@""];
+                        keyPath = tmp;
+                        break;
+                    }
+                }
                 if (keyPath.count > 1) {
                     propertyMeta->_mappedToKeyPath = keyPath;
                     [keyPathPropertyMetas addObject:propertyMeta];

YYModelTests/YYTestModelMapper.m

@@ -147,6 +147,10 @@
     model = [YYTestPropertyMapperModelCustom yy_modelWithJSON:json];
     XCTAssertTrue([model.desc4 isEqualToString:@"Apple"]);
     
+    json = @"{\".ext\":\"Apple\", \"name\":\"Apple\", \"count\":\"10\", \"desc1\":\"Apple\", \"desc2\":\"Apple\", \"desc3\":\"Apple\", \"desc4\":\"Apple\", \"modelID\":\"Apple\"}";
+    model = [YYTestPropertyMapperModelCustom yy_modelWithJSON:json];
+    XCTAssertTrue([model.desc4 isEqualToString:@"Apple"]);
+    
     json = @"{\"id\":\"abcd\"}";
     model = [YYTestPropertyMapperModelCustom yy_modelWithJSON:json];
     XCTAssertTrue([model.modelID isEqualToString:@"abcd"]);