[graph model] try to cast in quantitative test

better message
fixes #162

src/core/graph/utils.ts

@@ -1,6 +1,6 @@
 import Graph, { MultiGraph } from "graphology";
 import { Attributes } from "graphology-types";
-import { forEach, isNumber, keys, mapValues, omit, sortBy, take, uniq, values } from "lodash";
+import { forEach, isNil, isNumber, keys, mapValues, omit, sortBy, take, uniq, values } from "lodash";
 
 import { ItemType, Scalar } from "../types";
 import { toNumber, toScalar } from "../utils/casting";
@@ -328,11 +328,12 @@ export function countExistingValues(
     let nbCastIssues = 0;
     let nbMissingValues = 0;
     items.forEach((item) => {
-      if (item[fm.id] !== undefined) {
+      if (!isNil(item[fm.id])) {
         // attribute exists
         nbItems += 1;
         // is format correct?
-        if (fm.quantitative && typeof item[fm.id] !== "number") nbCastIssues += 1;
+        const value = item[fm.id];
+        if (fm.quantitative && typeof item[fm.id] !== "number" && !isNil(value) && isNaN(+value)) nbCastIssues += 1;
       } else nbMissingValues += 1;
     });
     return {

src/locales/dev.json

@@ -297,7 +297,7 @@
       },
       "warnings": {
         "missing": "{{nbValues}} missing values",
-        "wrong": "{{nbValues}} wrong values",
+        "wrong": "{{nbValues}} values are not quantitative",
         "allMissing": "No values in the graph"
       }
     },