Fix for empty string validation.

src/Squidex.Domain.Apps.Core.Operations/ValidateContent/Validators/RequiredStringValidator.cs

@@ -28,7 +28,7 @@ namespace Squidex.Domain.Apps.Core.ValidateContent.Validators
 
             var valueAsString = (string)value;
 
-            if (valueAsString == null || validateEmptyStrings && string.IsNullOrWhiteSpace(valueAsString))
+            if (valueAsString == null || (validateEmptyStrings && string.IsNullOrWhiteSpace(valueAsString)))
             {
                 addError(context.Path, "Field is required.");
             }

src/Squidex.Domain.Apps.Core.Operations/ValidateContent/ValidatorsFactory.cs

@@ -135,7 +135,7 @@ namespace Squidex.Domain.Apps.Core.ValidateContent
         {
             if (field.Properties.IsRequired)
             {
-                yield return new RequiredStringValidator();
+                yield return new RequiredStringValidator(true);
             }
 
             if (field.Properties.MinLength.HasValue || field.Properties.MaxLength.HasValue)

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/StringFieldTests.cs

@@ -49,6 +49,17 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
                 new[] { "Field is required." });
         }
 
+        [Fact]
+        public async Task Should_add_error_if_string_is_required_and_empty_string_is_passed()
+        {
+            var sut = Field(new StringFieldProperties { IsRequired = true });
+
+            await sut.ValidateAsync(CreateValue(string.Empty), errors);
+
+            errors.Should().BeEquivalentTo(
+                new[] { "Field is required." });
+        }
+
         [Fact]
         public async Task Should_add_error_if_string_is_shorter_than_min_length()
         {