Correctly check if validators are present (#11450)

Change-Id: Ibc0173f96a1000e709bd7ee90cccd500fad1a223

server/src/main/java/com/vaadin/ui/AbstractField.java

@@ -507,7 +507,7 @@ public abstract class AbstractField<T> extends AbstractComponent implements
             // Repaint is needed even when the client thinks that it knows the
             // new state if validity of the component may change
             if (repaintIsNotNeeded
-                    && (isRequired() || getValidators() != null || getConverter() != null)) {
+                    && (isRequired() || hasValidators() || getConverter() != null)) {
                 repaintIsNotNeeded = false;
             }
 
@@ -885,6 +885,10 @@ public abstract class AbstractField<T> extends AbstractComponent implements
         }
     }
 
+    private boolean hasValidators() {
+        return validators != null && !validators.isEmpty();
+    }
+
     /**
      * Removes the validator from the field.
      *