bz-62076 bz-39960 Expect the mapper to follow the FileNameMapper#mapFileName contract and move the check for null onto the entire returned array

src/main/org/apache/tools/ant/taskdefs/Copy.java

@@ -836,14 +836,11 @@ public class Copy extends Task {
         }
         for (int i = 0; i < toCopy.length; i++) {
             final String[] mappedFiles = mapper.mapFileName(toCopy[i].getName());
-            for (int j = 0; j < mappedFiles.length; j++) {
-                if (mappedFiles[j] == null) {
-                    throw new BuildException("Can't copy a resource without a"
-                                             + " name if the mapper doesn't"
-                                             + " provide one.");
-                }
+            if (mappedFiles == null) {
+                throw new BuildException("Can't copy a resource without a"
+                        + " name if the mapper doesn't"
+                        + " provide one.");
             }
-
             if (!enableMultipleMappings) {
                 map.put(toCopy[i],
                         new String[] {new File(toDir, mappedFiles[0]).getAbsolutePath()});