Fix possible NPE

Possible NPE when handling a pdf with
incorrect page rotation. Log and avoid using a default
setting.

SUP-1555, DEVSIX-832

Author: Samuel Huylebroeck

forms/src/main/java/com/itextpdf/forms/fields/PdfFormField.java

@@ -43,6 +43,7 @@ This file is part of the iText (R) project.
  */
 package com.itextpdf.forms.fields;
 
+import com.itextpdf.io.LogMessageConstant;
 import com.itextpdf.io.codec.Base64;
 import com.itextpdf.io.font.FontConstants;
 import com.itextpdf.io.font.PdfEncodings;
@@ -73,6 +74,8 @@ This file is part of the iText (R) project.
 import com.itextpdf.layout.property.Property;
 import com.itextpdf.layout.property.TextAlignment;
 import com.itextpdf.layout.property.VerticalAlignment;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
@@ -160,6 +163,7 @@ public class PdfFormField extends PdfObjectWrapper<PdfDictionary> {
     protected int rotation = 0;
     protected PdfFormXObject form;
     protected PdfAConformanceLevel pdfAConformanceLevel;
+    protected Logger formFieldLogger;
 
     protected static final String check = "0.8 0 0 0.8 0.3 0.5 cm 0 0 m\n" +
             "0.066 -0.026 l\n" +
@@ -235,6 +239,7 @@ public PdfFormField(PdfDictionary pdfObject) {
         super(pdfObject);
         ensureObjectIsAddedToDocument(pdfObject);
         setForbidRelease();
+        formFieldLogger = LoggerFactory.getLogger(this.getClass());
     }
 
     /**
@@ -1796,6 +1801,11 @@ public boolean regenerateField() {
                     //Copy Bounding box
                     bBox = new PdfArray(rect);
                 }
+                //Avoid NPE when handling corrupt pdfs
+                if(matrix == null){
+                    formFieldLogger.error(LogMessageConstant.INCORRECT_PAGEROTATION);
+                    matrix = new PdfArray(new double[]{1,0,0,1,0,0});
+                }
 
                 //Apply field rotation
                 float fieldRotation = 0;

io/src/main/java/com/itextpdf/io/LogMessageConstant.java

@@ -89,4 +89,5 @@ public final class LogMessageConstant {
     public static final String WRITER_ENCRYPTION_IS_IGNORED_APPEND = "Writer encryption will be ignored, because append mode is used. Document will preserve the original encryption (or will stay unencrypted)";
     public static final String WRITER_ENCRYPTION_IS_IGNORED_PRESERVE = "Writer encryption will be ignored, because preservation of encryption is enabled. Document will preserve the original encryption (or will stay unencrypted)";
     public static final String XREF_ERROR = "Error occurred while reading cross reference table. Cross reference table will be rebuilt.";
+    public static final String INCORRECT_PAGEROTATION = "Encounterd a page rotation that was not a multiple of 90°/ (Pi/2) when generating default appearances for form fields";
 }