Create empty PdfArray for fields in acroform when fields entry doesn't exist, warn with logging message

DEVSIX-1405

Author: LodrKumquat

forms/src/main/java/com/itextpdf/forms/PdfAcroForm.java

@@ -819,7 +819,13 @@ public void replaceField(String name, PdfFormField field) {
      * @return a {@link PdfArray} of field dictionaries
      */
     protected PdfArray getFields() {
-        return getPdfObject().getAsArray(PdfName.Fields);
+        PdfArray fields = getPdfObject().getAsArray(PdfName.Fields);
+        if (fields == null) {
+            logger.warn(LogMessageConstant.NO_FIELDS_IN_ACROFORM);
+            fields = new PdfArray();
+            getPdfObject().put(PdfName.Fields, fields);
+        }
+        return fields;
     }
 
     @Override

forms/src/test/java/com/itextpdf/forms/PdfFormFieldTest.java

@@ -46,6 +46,7 @@ This file is part of the iText (R) project.
 import com.itextpdf.forms.fields.PdfChoiceFormField;
 import com.itextpdf.forms.fields.PdfFormField;
 import com.itextpdf.forms.fields.PdfTextFormField;
+import com.itextpdf.io.LogMessageConstant;
 import com.itextpdf.io.source.ByteArrayOutputStream;
 import com.itextpdf.kernel.geom.Rectangle;
 import com.itextpdf.kernel.pdf.PdfDocument;
@@ -54,6 +55,8 @@ This file is part of the iText (R) project.
 import com.itextpdf.kernel.pdf.PdfWriter;
 import com.itextpdf.kernel.utils.CompareTool;
 import com.itextpdf.test.ExtendedITextTest;
+import com.itextpdf.test.annotations.LogMessage;
+import com.itextpdf.test.annotations.LogMessages;
 import com.itextpdf.test.annotations.type.IntegrationTest;
 import org.junit.Assert;
 import org.junit.BeforeClass;
@@ -339,4 +342,24 @@ public void autoScaleFontSizeInFormFields() throws IOException, InterruptedExcep
             Assert.fail(errorMessage);
         }
     }
+
+    @Test
+    @LogMessages(messages = {@LogMessage(messageTemplate = LogMessageConstant.NO_FIELDS_IN_ACROFORM)})
+    public void acroFieldDictionaryNoFields() throws IOException, InterruptedException {
+        String outPdf = destinationFolder + "acroFieldDictionaryNoFields.pdf";
+        String cmpPdf = sourceFolder + "cmp_acroFieldDictionaryNoFields.pdf";
+
+        PdfWriter writer = new PdfWriter(outPdf);
+        PdfReader reader = new PdfReader(sourceFolder + "acroFieldDictionaryNoFields.pdf");
+        PdfDocument pdfDoc = new PdfDocument(reader, writer);
+
+        PdfAcroForm form = PdfAcroForm.getAcroForm(pdfDoc, true);
+        pdfDoc.close();
+
+        CompareTool compareTool = new CompareTool();
+        String errorMessage = compareTool.compareByContent(outPdf, cmpPdf, destinationFolder, "diff_");
+        if (errorMessage != null) {
+            Assert.fail(errorMessage);
+        }
+    }
 }

forms/src/test/resources/com/itextpdf/forms/PdfFormFieldTest/acroFieldDictionaryNoFields.pdf

@@ -85,6 +85,7 @@ public final class LogMessageConstant {
     public static final String CALCULATE_HASHCODE_FOR_MODIFIED_PDFNUMBER = "Calculate hashcode for modified PdfNumber.";
     public static final String MAKE_COPY_OF_CATALOG_DICTIONARY_IS_FORBIDDEN = "Make copy of Catalog dictionary is forbidden.";
     public static final String NAME_ALREADY_EXISTS_IN_THE_NAME_TREE = "Name \"{0}\" already exists in the name tree; old value will be replaced by the new one.";
+    public static final String NO_FIELDS_IN_ACROFORM = "Required AcroForm entry /Fields does not exist in the document. Empty array /Fields will be created.";
     public static final String NOT_TAGGED_PAGES_IN_TAGGED_DOCUMENT = "Not tagged pages are copied to the tagged document. Destination document now may contain not tagged content.";
     public static final String NUM_TREE_SHALL_NOT_END_WITH_KEY = "Number tree ends with a key which is invalid according to the PDF specification.";
     public static final String PDF_READER_CLOSING_FAILED = "PdfReader closing failed due to the error occurred!";