Replace PyUnicode_FromUnicode(NULL, 0) by PyUnicode_New(0, 0)

Create an empty string with the new Unicode API.

Modules/cjkcodecs/multibytecodec.c

@@ -633,7 +633,7 @@ MultibyteCodec_Decode(MultibyteCodecObject *self,
     if (datalen == 0) {
         PyBuffer_Release(&pdata);
         ERROR_DECREF(errorcb);
-        return make_tuple(PyUnicode_FromUnicode(NULL, 0), 0);
+        return make_tuple(PyUnicode_New(0, 0), 0);
     }
 
     buf.excobj = NULL;
@@ -1265,7 +1265,7 @@ mbstreamreader_iread(MultibyteStreamReaderObject *self,
     Py_ssize_t rsize, finalsize = 0;
 
     if (sizehint == 0)
-        return PyUnicode_FromUnicode(NULL, 0);
+        return PyUnicode_New(0, 0);
 
     buf.outobj = buf.excobj = NULL;
     cres = NULL;

Objects/stringlib/unicode_format.h

@@ -79,7 +79,7 @@ Py_LOCAL_INLINE(PyObject *)
 SubString_new_object_or_empty(SubString *str)
 {
     if (str->str == NULL) {
-        return PyUnicode_FromUnicode(NULL, 0);
+        return PyUnicode_New(0, 0);
     }
     return SubString_new_object(str);
 }