diff --git a/web/app/cad/craft/intializeBySchema.js b/web/app/cad/craft/intializeBySchema.js
index 9a5acfe5..2014e860 100644
--- a/web/app/cad/craft/intializeBySchema.js
+++ b/web/app/cad/craft/intializeBySchema.js
@@ -26,7 +26,7 @@ export default function initializeBySchema(schema, context) {
     } else if (md.type === 'object') {
       val = initializeBySchema(md.schema, context);
     } else if (md.type === 'number') {
-      val = md.defaultValue + '';
+      val = md.defaultValue;
     } else {
       val = md.defaultValue;
     }
diff --git a/web/app/cad/craft/materializeParams.js b/web/app/cad/craft/materializeParams.js
index 0d4c053c..967af637 100644
--- a/web/app/cad/craft/materializeParams.js
+++ b/web/app/cad/craft/materializeParams.js
@@ -10,14 +10,19 @@ export default function materializeParams(services, params, schema, result, erro
       continue;
     }
     let value = params[field];
-    if (value === undefined) {
+    if (value === undefined || value === null || value === '') {
       if (!md.optional) {
         errors.push({path: [...parentPath, field], message: 'required'});
       }
     } else {
       if (md.type === 'number') {
         try {
-          value = services.expressions.evaluateExpression(value);  
+          const valueType =  typeof value;
+          if (valueType === 'string') {
+            value = services.expressions.evaluateExpression(value);  
+          } else if (valueType !== 'number') {
+            errors.push({path: [...parentPath, field], message: 'invalid value'});
+          }
         } catch (e) {
           errors.push({path: [...parentPath, field], message: 'unable to evaluate expression'});
         }