PROGMEM attribute ignored for implicit pointer initialization

Windows Arduino IDE 1.8.9, default settings.

**Description:**
bellow both statements are identical. In both cases we get array of pointers, where all elements will be NULL pointers. And both variables occupies identical size 20 byte in SRAM
`const char *const list[10];`
`const char *const list[10] = {NULL};`

BUT

**Actual behavior:**
if we will try put it in Flash then for first one, PROGMEM attribute is ignored and it will be placed only in SRAM instead of PROGMEM
`const PROGMEM char *const list[10]; // will be placed in SRAM. progmem ignored`
`const PROGMEM char *const list[10] = {NULL}; // will be placed in PROGMEM`

**Expected behavior:**
`const PROGMEM char *const list[10];` should be placed in Flash

Reproduce the two declarations in Windows Arduino IDE 1.8.9 and compare their SRAM and Flash placement. Investigate how PROGMEM is handled for an implicitly initialized pointer array; done means the uninitialized form is placed in Flash like the {NULL} form without changing the expected NULL elements.

Written by the indexing model from the issue text.