diff --git a/src/main/org/apache/tools/ant/taskdefs/Copy.java b/src/main/org/apache/tools/ant/taskdefs/Copy.java
index 477792e72..c4a112b70 100644
--- a/src/main/org/apache/tools/ant/taskdefs/Copy.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Copy.java
@@ -788,6 +788,9 @@ public class Copy extends Task {
         for (int i = 0; i < toCopy.length; i++) {
             final File src = new File(fromDir, toCopy[i]);
             final String[] mappedFiles = mapper.mapFileName(toCopy[i]);
+            if (mappedFiles == null || mappedFiles.length == 0) {
+                continue;
+            }
 
             if (!enableMultipleMappings) {
                 map.put(src.getAbsolutePath(),
@@ -831,7 +834,7 @@ public class Copy extends Task {
         }
         for (int i = 0; i < toCopy.length; i++) {
             final String[] mappedFiles = mapper.mapFileName(toCopy[i].getName());
-            if (mappedFiles == null) {
+            if (mappedFiles == null || mappedFiles.length == 0) {
                 throw new BuildException("Can't copy a resource without a"
                         + " name if the mapper doesn't"
                         + " provide one.");
diff --git a/src/main/org/apache/tools/ant/taskdefs/CopyPath.java b/src/main/org/apache/tools/ant/taskdefs/CopyPath.java
index 53596fd98..bad9e5d93 100644
--- a/src/main/org/apache/tools/ant/taskdefs/CopyPath.java
+++ b/src/main/org/apache/tools/ant/taskdefs/CopyPath.java
@@ -182,6 +182,9 @@ public class CopyPath extends Task {
             String sourceFileName = sourceFiles[sources];
             File sourceFile = new File(sourceFileName);
             String[] toFiles = (String[]) mapper.mapFileName(sourceFileName);
+            if (toFiles == null) {
+                continue;
+            }
 
             for (int i = 0; i < toFiles.length; i++) {
                 String destFileName = toFiles[i];
diff --git a/src/main/org/apache/tools/ant/taskdefs/Rmic.java b/src/main/org/apache/tools/ant/taskdefs/Rmic.java
index c42ad419c..aa762b188 100644
--- a/src/main/org/apache/tools/ant/taskdefs/Rmic.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Rmic.java
@@ -705,6 +705,9 @@ public class Rmic extends MatchingTask {
         String classFileName = classname.replace('.', File.separatorChar)
             + ".class";
         String[] generatedFiles = adapter.getMapper().mapFileName(classFileName);
+        if (generatedFiles == null) {
+            return;
+        }
 
         for (String generatedFile : generatedFiles) {
             if (!generatedFile.endsWith(".class")) {
diff --git a/src/main/org/apache/tools/ant/taskdefs/optional/Native2Ascii.java b/src/main/org/apache/tools/ant/taskdefs/optional/Native2Ascii.java
index 2c7e9de78..b50674cf1 100644
--- a/src/main/org/apache/tools/ant/taskdefs/optional/Native2Ascii.java
+++ b/src/main/org/apache/tools/ant/taskdefs/optional/Native2Ascii.java
@@ -256,7 +256,10 @@ public class Native2Ascii extends MatchingTask {
             + (count != 1 ? "s" : "") + " from ";
         log(message + srcDir + " to " + destDir);
         for (int i = 0; i < files.length; i++) {
-            convert(files[i], m.mapFileName(files[i])[0]);
+            String[] dest = m.mapFileName(files[i]);
+            if (dest != null && dest.length > 0) {
+                convert(files[i], dest[0]);
+            }
         }
     }
 
diff --git a/src/main/org/apache/tools/ant/types/mappers/CutDirsMapper.java b/src/main/org/apache/tools/ant/types/mappers/CutDirsMapper.java
index 052a0379e..1b9839181 100644
--- a/src/main/org/apache/tools/ant/types/mappers/CutDirsMapper.java
+++ b/src/main/org/apache/tools/ant/types/mappers/CutDirsMapper.java
@@ -66,6 +66,9 @@ public class CutDirsMapper implements FileNameMapper {
             throw new BuildException("dirs must be set to a positive number");
         }
         final char fileSep = File.separatorChar;
+        if (sourceFileName == null) {
+            return null;
+        }
         final String fileSepCorrected =
             sourceFileName.replace('/', fileSep).replace('\\', fileSep);
         int nthMatch = fileSepCorrected.indexOf(fileSep);
diff --git a/src/main/org/apache/tools/ant/types/mappers/FilterMapper.java b/src/main/org/apache/tools/ant/types/mappers/FilterMapper.java
index b4c07e942..3a0109bb6 100644
--- a/src/main/org/apache/tools/ant/types/mappers/FilterMapper.java
+++ b/src/main/org/apache/tools/ant/types/mappers/FilterMapper.java
@@ -66,6 +66,9 @@ public class FilterMapper extends FilterChain implements FileNameMapper {
      */
     @Override
     public String[] mapFileName(String sourceFileName) {
+        if (sourceFileName == null) {
+            return null;
+        }
         try {
             Reader stringReader = new StringReader(sourceFileName);
             ChainReaderHelper helper = new ChainReaderHelper();
diff --git a/src/main/org/apache/tools/ant/util/ChainedMapper.java b/src/main/org/apache/tools/ant/util/ChainedMapper.java
index 8b3e32f76..cec4f2e48 100644
--- a/src/main/org/apache/tools/ant/util/ChainedMapper.java
+++ b/src/main/org/apache/tools/ant/util/ChainedMapper.java
@@ -32,6 +32,9 @@ public class ChainedMapper extends ContainerMapper {
     /** {@inheritDoc}. */
     @Override
     public String[] mapFileName(String sourceFileName) {
+        // we invoke the chain even if the sourceFileName is null. Some
+        // resources have a null name and users may use a mapper like
+        // MergeMapper to provide a name for it.
         String[] result = getMappers().stream()
             .reduce(new String[] { sourceFileName }, (i, m) -> Stream.of(i)
                 .map(m::mapFileName).filter(Objects::nonNull).flatMap(Stream::of).toArray(String[]::new),
diff --git a/src/main/org/apache/tools/ant/util/FileNameMapper.java b/src/main/org/apache/tools/ant/util/FileNameMapper.java
index bbd826141..ec85f9d5d 100644
--- a/src/main/org/apache/tools/ant/util/FileNameMapper.java
+++ b/src/main/org/apache/tools/ant/util/FileNameMapper.java
@@ -52,7 +52,9 @@ public interface FileNameMapper {
      * omit the source file in question.</p>
      *
      * @param sourceFileName the name of the source file relative to
-     *                       some given basedirectory.
+     *                       some given basedirectory. Might be {@code
+     *                       null} for resources that don't provide a
+     *                       name.
      * @return an array of strings if the rule applies to the source file, or
      *         null if it does not.
      */
diff --git a/src/main/org/apache/tools/ant/util/FlatFileNameMapper.java b/src/main/org/apache/tools/ant/util/FlatFileNameMapper.java
index 8465c7869..37383b631 100644
--- a/src/main/org/apache/tools/ant/util/FlatFileNameMapper.java
+++ b/src/main/org/apache/tools/ant/util/FlatFileNameMapper.java
@@ -53,5 +53,7 @@ public class FlatFileNameMapper implements FileNameMapper {
     @Override
     public String[] mapFileName(String sourceFileName) {
         return new String[] { new java.io.File(sourceFileName).getName() };
+        return sourceFileName == null ? null
+            : new String[] {new java.io.File(sourceFileName).getName()};
     }
 }
diff --git a/src/main/org/apache/tools/ant/util/GlobPatternMapper.java b/src/main/org/apache/tools/ant/util/GlobPatternMapper.java
index 8e470ac8d..63a8f36e0 100644
--- a/src/main/org/apache/tools/ant/util/GlobPatternMapper.java
+++ b/src/main/org/apache/tools/ant/util/GlobPatternMapper.java
@@ -155,6 +155,9 @@ public class GlobPatternMapper implements FileNameMapper {
      */
     @Override
     public String[] mapFileName(String sourceFileName) {
+        if (sourceFileName == null) {
+            return null;
+        }
         String modName = modifyName(sourceFileName);
         if (fromPrefix == null
             || (sourceFileName.length() < (prefixLength + postfixLength))
diff --git a/src/main/org/apache/tools/ant/util/RegexpPatternMapper.java b/src/main/org/apache/tools/ant/util/RegexpPatternMapper.java
index 82bc109db..495a644b9 100644
--- a/src/main/org/apache/tools/ant/util/RegexpPatternMapper.java
+++ b/src/main/org/apache/tools/ant/util/RegexpPatternMapper.java
@@ -115,6 +115,9 @@ public class RegexpPatternMapper implements FileNameMapper {
      */
     @Override
     public String[] mapFileName(String sourceFileName) {
+        if (sourceFileName == null) {
+            return null;
+        }
         if (handleDirSep) {
             if (sourceFileName.indexOf("\\") != -1) {
                 sourceFileName = sourceFileName.replace('\\', '/');