PDFBOX-6187: avoid NPE

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/branches/2.0@1932849 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

pdfbox/src/main/java/org/apache/pdfbox/pdmodel/interactive/form/AppearanceGeneratorHelper.java

@@ -490,10 +490,12 @@ private void insertGeneratedAppearance(PDAnnotationWidget widget, PDAppearanceSt
 
         // get the font
         PDFont font = defaultAppearance.getFont();
-        if (font == null) {
+        if (font == null)
+        {
             throw new IllegalArgumentException("font is null, check whether /DA entry is incomplete or incorrect");
         }
-        if (font.getName().contains("+")) {
+        if (font.getName() != null && font.getName().contains("+"))
+        {
             LOG.warn("Font '" + defaultAppearance.getFontName().getName() + "' of field '"
                     + field.getFullyQualifiedName() + "' contains subsetted font '" + font.getName() + "'");
             LOG.warn("This may bring trouble with PDField.setValue(), PDAcroForm.flatten() or "