Fixing issue with min/max in numbers.

packages/standard-components/src/forms/validation.js

@@ -77,6 +77,9 @@ const lengthConstraint = maxLength => value => {
 }
 
 const numericalConstraint = (constraint, error) => value => {
+  if (value == null || value === "") {  
+    return null
+  }
   if (isNaN(value)) {
     return "Must be a number"
   }