fix null opacity

partly revert 952385 - since ´null´ is actually used in ternary fields.
Remove null opacity from the testcase. It should be either unset or a
numeric value.

umap/static/umap/js/umap.core.js

@@ -161,7 +161,7 @@ L.Util.detectFileType = (f) => {
 }
 
 L.Util.usableOption = (options, option) =>
-  options[option] !== undefined && options[option] !== '' && options[option] !== null
+  options[option] !== undefined && options[option] !== ''
 
 L.Util.greedyTemplate = (str, data, ignore) => {
   function getValue(data, path) {

umap/static/umap/test/_pre.js

@@ -92,14 +92,12 @@ var defaultDatalayerData = function (custom) {
     displayOnLoad: true,
     id: 62,
     pictogram_url: null,
-    opacity: null,
     weight: null,
     fillColor: '',
     color: '',
     stroke: true,
     smoothFactor: null,
     dashArray: '',
-    fillOpacity: null,
     fill: true,
   }
   return L.extend({}, _default, custom)