Use nullptr

Marlin/src/lcd/extui/lib/ftdi_eve_touch_ui/ftdi_eve_lib/extended/unicode/western_char_set.cpp

       base_char   = base_special ? NO_DOT_I : std_char;
     }
 
-    // If cmd != NULL, draw the glyph to the screen
+    // If cmd != nullptr, draw the glyph to the screen
     if (cmd) {
       ext_vertex2ii(*cmd, x, y, base_special ? alt_font : std_font, base_char);
       if (accent_char)

Marlin/src/lcd/extui/lib/ftdi_eve_touch_ui/ftdi_eve_lib/extras/poly_ui.h

         if (start_x != eol)
           close_loop();
         else
-          p = NULL;
+          p = nullptr;
       }
       else {
         x = pgm_read_word_far(p++);
       }
     }
 
-    bool has_more()       { return p != NULL; }
+    bool has_more()       { return p != nullptr; }
     bool end_of_loop()    { return start_x == eol; }
 };
 

Marlin/src/lcd/tft/tft_string.h

 
     static font_t *font() { return font_header; };
     static uint16_t font_height() { return font_header->FontAscent - font_header->FontDescent; }
-    static glyph_t *glyph(uint8_t character) { return glyphs[character] == NULL ? glyphs[0x3F] : glyphs[character]; }  /* Use '?' for unknown glyphs */
+    static glyph_t *glyph(uint8_t character) { return glyphs[character] ?: glyphs[0x3F]; }  /* Use '?' for unknown glyphs */
     static inline glyph_t *glyph(uint8_t *character) { return glyph(*character); }
 
     static void set();
     static void add(uint8_t character) { add_character(character); eol(); }
     static void add(uint8_t *string);
-    static void add(uint8_t *string, int8_t index, uint8_t *itemString = NULL);
+    static void add(uint8_t *string, int8_t index, uint8_t *itemString=nullptr);
     static void set(uint8_t *string) { set(); add(string); };
-    static void set(uint8_t *string, int8_t index, const char *itemString = NULL) { set(); add(string, index, (uint8_t *)itemString); };
+    static void set(uint8_t *string, int8_t index, const char *itemString=nullptr) { set(); add(string, index, (uint8_t *)itemString); };
     static inline void set(const char *string) { set((uint8_t *)string); }
-    static inline void set(const char *string, int8_t index, const char *itemString = NULL) { set((uint8_t *)string, index, itemString); }
+    static inline void set(const char *string, int8_t index, const char *itemString=nullptr) { set((uint8_t *)string, index, itemString); }
     static inline void add(const char *string) { add((uint8_t *)string); }
 
-    static void trim(uint8_t character = 0x20);
-    static void rtrim(uint8_t character = 0x20);
-    static void ltrim(uint8_t character = 0x20);
+    static void trim(uint8_t character=0x20);
+    static void rtrim(uint8_t character=0x20);
+    static void ltrim(uint8_t character=0x20);
     static uint16_t width() { return span; }
     static uint8_t *string() { return data; }
     static uint16_t center(uint16_t width) { return span > width ? 0 : (width - span) / 2; }