Config: allow to set maps on null value

Also, now, if ipfs config foo.bar has value of anything that is not map (0, "0", 0.1),
then ipfs config foo.bar.baz now returns an error instead of a panic

License: MIT
Signed-off-by: rht <rhtbot@gmail.com>

repo/common/common.go

@@ -7,12 +7,20 @@ import (
 
 func MapGetKV(v map[string]interface{}, key string) (interface{}, error) {
 	var ok bool
+	var mcursor map[string]interface{}
 	var cursor interface{} = v
+
 	parts := strings.Split(key, ".")
 	for i, part := range parts {
-		cursor, ok = cursor.(map[string]interface{})[part]
-		if !ok {
 		sofar := strings.Join(parts[:i], ".")
+
+		mcursor, ok = cursor.(map[string]interface{})
+		if !ok {
+			return nil, fmt.Errorf("%s key is not a map", sofar)
+		}
+
+		cursor, ok = mcursor[part]
+		if !ok {
 			return nil, fmt.Errorf("%s key has no attributes", sofar)
 		}
 	}
@@ -39,7 +47,7 @@ func MapSetKV(v map[string]interface{}, key string, value interface{}) error {
 		}
 
 		cursor, ok = mcursor[part]
-		if !ok { // create map if this is empty
+		if !ok || cursor == nil { // create map if this is empty or is null
 			mcursor[part] = map[string]interface{}{}
 			cursor = mcursor[part]
 		}