TIKA-4811: Add null check (#2999)

Author: L3odr0id

tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-pdf-module/src/main/java/org/apache/tika/parser/pdf/AbstractPDF2XHTML.java

@@ -536,7 +536,8 @@ void doOCROnCurrentPage(PDPage pdPage, PDFParserConfig.OCR_STRATEGY ocrStrategy)
             return;
         }
         MediaType ocrImageMediaType = MediaType.image("ocr-" + config.getOcrImageFormatName());
-        if (!ocrParser.getSupportedTypes(context).contains(ocrImageMediaType)) {
+        Set<MediaType> supportedTypes = ocrParser.getSupportedTypes(context);
+        if (supportedTypes == null || !supportedTypes.contains(ocrImageMediaType)) {
             if (ocrStrategy == OCR_ONLY || ocrStrategy == OCR_AND_TEXT_EXTRACTION) {
                 throw new TikaException(
                         "" + "I regret that I couldn't find an OCR parser to handle " +