Add tests for PdfDocument with missing, null and not PdfString producer

DEVSIX-5084

Autoported commit.
Original commit hash: [1a88e77a3]

Author: BezrukovM

itext.tests/itext.kernel.tests/itext/kernel/pdf/PdfDocumentTest.cs

@@ -69,6 +69,55 @@ public static void BeforeClass() {
             CreateOrClearDestinationFolder(DESTINATION_FOLDER);
         }
 
+        [NUnit.Framework.Test]
+        public virtual void MissingProducerTest() {
+            String inputFile = SOURCE_FOLDER + "missingProducer.pdf";
+            using (PdfDocument document = new PdfDocument(new PdfReader(inputFile))) {
+                PdfDocumentInfo documentInfo = document.GetDocumentInfo();
+                NUnit.Framework.Assert.IsNull(documentInfo.GetPdfObject().Get(PdfName.Producer));
+                NUnit.Framework.Assert.IsNull(documentInfo.GetProducer());
+            }
+            using (PdfDocument document_1 = new PdfDocument(new PdfReader(inputFile), new PdfWriter(new MemoryStream()
+                ))) {
+                PdfDocumentInfo documentInfo = document_1.GetDocumentInfo();
+                NUnit.Framework.Assert.IsNotNull(documentInfo.GetPdfObject().Get(PdfName.Producer));
+                NUnit.Framework.Assert.IsNotNull(document_1.GetDocumentInfo().GetProducer());
+            }
+        }
+
+        [NUnit.Framework.Test]
+        public virtual void NullProducerTest() {
+            String inputFile = SOURCE_FOLDER + "nullProducer.pdf";
+            using (PdfDocument document = new PdfDocument(new PdfReader(inputFile))) {
+                PdfDocumentInfo documentInfo = document.GetDocumentInfo();
+                NUnit.Framework.Assert.AreEqual(PdfNull.PDF_NULL, documentInfo.GetPdfObject().Get(PdfName.Producer));
+                NUnit.Framework.Assert.IsNull(documentInfo.GetProducer());
+            }
+            using (PdfDocument document_1 = new PdfDocument(new PdfReader(inputFile), new PdfWriter(new MemoryStream()
+                ))) {
+                PdfDocumentInfo documentInfo = document_1.GetDocumentInfo();
+                NUnit.Framework.Assert.IsNotNull(documentInfo.GetPdfObject().Get(PdfName.Producer));
+                NUnit.Framework.Assert.IsNotNull(document_1.GetDocumentInfo().GetProducer());
+            }
+        }
+
+        [NUnit.Framework.Test]
+        public virtual void NameProducerTest() {
+            String inputFile = SOURCE_FOLDER + "nameProducer.pdf";
+            using (PdfDocument document = new PdfDocument(new PdfReader(inputFile))) {
+                PdfDocumentInfo documentInfo = document.GetDocumentInfo();
+                NUnit.Framework.Assert.AreEqual(new PdfName("producerAsName"), documentInfo.GetPdfObject().Get(PdfName.Producer
+                    ));
+                NUnit.Framework.Assert.IsNull(documentInfo.GetProducer());
+            }
+            using (PdfDocument document_1 = new PdfDocument(new PdfReader(inputFile), new PdfWriter(new MemoryStream()
+                ))) {
+                PdfDocumentInfo documentInfo = document_1.GetDocumentInfo();
+                NUnit.Framework.Assert.IsNotNull(documentInfo.GetPdfObject().Get(PdfName.Producer));
+                NUnit.Framework.Assert.IsNotNull(document_1.GetDocumentInfo().GetProducer());
+            }
+        }
+
         [NUnit.Framework.Test]
         public virtual void WritingVersionTest01() {
             // There is a possibility to override version in stamping mode

itext.tests/itext.kernel.tests/resources/itext/kernel/pdf/PdfDocumentTest/missingProducer.pdf

@@ -2272,7 +2272,7 @@ private void UpdateProducerInInfoDictionary() {
             else {
                 if (info.GetPdfObject().ContainsKey(PdfName.Producer)) {
                     PdfString producerPdfStr = info.GetPdfObject().GetAsString(PdfName.Producer);
-                    producer = producerPdfStr != null ? producerPdfStr.ToUnicodeString() : null;
+                    producer = producerPdfStr == null ? null : producerPdfStr.ToUnicodeString();
                 }
                 producer = AddModifiedPostfix(producer);
             }

itext.tests/itext.kernel.tests/resources/itext/kernel/pdf/PdfDocumentTest/nameProducer.pdf

@@ -1 +1 @@
-090af8f2c31512fb80c559ee5dd60c15ee97fc28
+1a88e77a3ad86d8caa576b20ef41863b293f6403