optional for mapdata

Replace assign with optional, it has better support for JSON features.

Author: ehughsbaird

src/mapdata.cpp

@@ -8,7 +8,6 @@
 #include <unordered_map>
 #include <utility>
 
-#include "assign.h"
 #include "avatar.h"
 #include "calendar.h"
 #include "character.h"
@@ -514,9 +513,9 @@ bool furn_workbench_info::load( const JsonObject &jsobj, std::string_view member
 {
     JsonObject j = jsobj.get_object( member );
 
-    assign( j, "multiplier", multiplier );
-    assign( j, "mass", allowed_mass );
-    assign( j, "volume", allowed_volume );
+    optional( j, false, "multiplier", multiplier, 1.0f );
+    optional( j, false, "mass", allowed_mass, units::mass::max() );
+    optional( j, false, "volume", allowed_volume, units::volume::max() );
 
     return true;
 }
@@ -528,10 +527,10 @@ bool plant_data::load( const JsonObject &jsobj, std::string_view member )
 {
     JsonObject j = jsobj.get_object( member );
 
-    assign( j, "transform", transform );
-    assign( j, "base", base );
-    assign( j, "growth_multiplier", growth_multiplier );
-    assign( j, "harvest_multiplier", harvest_multiplier );
+    optional( j, false, "transform", transform, furn_str_id::NULL_ID() );
+    optional( j, false, "base", base, furn_str_id::NULL_ID() );
+    optional( j, false, "growth_multiplier", growth_multiplier, 1.0f );
+    optional( j, false, "harvest_multiplier", harvest_multiplier, 1.0f );
 
     return true;
 }
@@ -1196,7 +1195,7 @@ void ter_t::load( const JsonObject &jo, const std::string &src )
 {
     map_data_common_t::load( jo, src );
     optional( jo, was_loaded, "move_cost", movecost );
-    assign( jo, "max_volume", max_volume, src == "dda" );
+    optional( jo, was_loaded, "max_volume", max_volume, DEFAULT_TILE_VOLUME );
     optional( jo, was_loaded, "trap", trap_id_str );
     optional( jo, was_loaded, "heat_radiation", heat_radiation );