diff --git a/packages/builder/src/helpers/helpers.js b/packages/builder/src/helpers/helpers.js
index 9b0fa51a52..72c034d9a6 100644
--- a/packages/builder/src/helpers/helpers.js
+++ b/packages/builder/src/helpers/helpers.js
@@ -17,7 +17,12 @@ export const convertCamel = str => {
 
 export const pipe = (arg, funcs) => flow(funcs)(arg)
 
-export const capitalise = s => s.substring(0, 1).toUpperCase() + s.substring(1)
+export const capitalise = s => {
+  if (!s) {
+    return s
+  }
+  return s.substring(0, 1).toUpperCase() + s.substring(1)
+}
 
 export const lowercase = s => s.substring(0, 1).toLowerCase() + s.substring(1)
 
diff --git a/packages/builder/src/helpers/validation/yup/index.js b/packages/builder/src/helpers/validation/yup/index.js
index 9b38adbf9d..c064ffa583 100644
--- a/packages/builder/src/helpers/validation/yup/index.js
+++ b/packages/builder/src/helpers/validation/yup/index.js
@@ -28,7 +28,9 @@ export const createValidationStore = () => {
     let propertyValidator
     switch (type) {
       case "number":
-        propertyValidator = number()
+        propertyValidator = number().transform(value =>
+          isNaN(value) ? undefined : value
+        )
         break
       case "email":
         propertyValidator = string().email()