[CSV-239] Cannot get headers in column order from CSVRecord.

* fix exception messages

Author: davidmoten

src/main/java/org/apache/commons/csv/CSVParser.java

@@ -490,11 +490,10 @@ private Headers createHeaderMapAndHeaderNames() throws IOException {
                     final boolean emptyHeader = header == null || header.trim().isEmpty();
                     if (containsHeader && !emptyHeader && !this.format.getAllowDuplicateHeaderNames()) {
                     	throw new IllegalArgumentException("The header contains a duplicate name: \"" + header
-                                + "\" in " + Arrays.toString(headerRecord) + ". If your data is valid then use CSVFormat.withAllowDuplicateHeaderNames().");
+                                + "\" in " + Arrays.toString(headerRecord) + ". If this is valid then use CSVFormat.withAllowDuplicateHeaderNames().");
                     }
-                    if (containsHeader && (emptyHeader && !this.format.getAllowMissingColumnNames())) {
-                        throw new IllegalArgumentException("The header contains a duplicate name: \"" + header
-                                + "\" in " + Arrays.toString(headerRecord));
+                    if (containsHeader && emptyHeader && !this.format.getAllowMissingColumnNames()) {
+                        throw new IllegalArgumentException("A header name is missing in " + Arrays.toString(headerRecord));
                     }
                     if (header != null) {
                         hdrMap.put(header, Integer.valueOf(i));