diff --git a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/AvroTransformer.java b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/AvroTransformer.java
index 94bf12c7..3647ca12 100644
--- a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/AvroTransformer.java
+++ b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/AvroTransformer.java
@@ -55,9 +55,8 @@ public StreamSpliterator createSpliterator(final IOSupplier<InputStream> inputSt
             private final DatumReader<GenericRecord> datumReader = new GenericDatumReader<>();
 
             @Override
-            protected InputStream inputOpened(final InputStream input) throws IOException {
+            protected void inputOpened(final InputStream input) throws IOException {
                 dataFileStream = new DataFileStream<>(input, datumReader);
-                return input;
             }
 
             @Override
diff --git a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/ByteArrayTransformer.java b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/ByteArrayTransformer.java
index 43059cc0..b33cb127 100644
--- a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/ByteArrayTransformer.java
+++ b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/ByteArrayTransformer.java
@@ -52,9 +52,10 @@ public StreamSpliterator createSpliterator(final IOSupplier<InputStream> inputSt
         // The max buffer size for the byte array the default is 4096 if not set by the user.
         final int maxBufferSize = sourceConfig.getTransformerMaxBufferSize();
         return new StreamSpliterator(LOGGER, inputStreamIOSupplier) {
+
             @Override
-            protected InputStream inputOpened(final InputStream input) {
-                return input;
+            protected void inputOpened(final InputStream input) {
+
             }
 
             @Override
@@ -102,9 +103,9 @@ protected void doClose() {
             }
 
             @Override
-            protected InputStream inputOpened(final InputStream input) throws IOException {
-                return InputStream.nullInputStream();
+            protected void inputOpened(final InputStream input) {
             }
+
         };
     }
 
diff --git a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/JsonTransformer.java b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/JsonTransformer.java
index 56eb8e81..7b39552a 100644
--- a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/JsonTransformer.java
+++ b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/JsonTransformer.java
@@ -55,9 +55,9 @@ public StreamSpliterator createSpliterator(final IOSupplier<InputStream> inputSt
             BufferedReader reader;
 
             @Override
-            protected InputStream inputOpened(final InputStream input) throws IOException {
+            protected void inputOpened(final InputStream input) {
                 reader = new BufferedReader(new InputStreamReader(input, StandardCharsets.UTF_8));
-                return input;
+
             }
 
             @Override
diff --git a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/ParquetTransformer.java b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/ParquetTransformer.java
index 6a4d5d1b..679d70b3 100644
--- a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/ParquetTransformer.java
+++ b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/ParquetTransformer.java
@@ -68,7 +68,7 @@ public StreamSpliterator createSpliterator(final IOSupplier<InputStream> inputSt
             private File parquetFile;
 
             @Override
-            protected InputStream inputOpened(final InputStream input) throws IOException {
+            protected void inputOpened(final InputStream input) throws IOException {
                 final String timestamp = String.valueOf(Instant.now().toEpochMilli());
 
                 try {
@@ -84,7 +84,7 @@ protected InputStream inputOpened(final InputStream input) throws IOException {
                     IOUtils.copy(input, outputStream); // Copy input stream to temporary file
                 }
                 reader = AvroParquetReader.<GenericRecord>builder(new LocalInputFile(parquetFile.toPath())).build();
-                return input;
+
             }
 
             @Override
diff --git a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/Transformer.java b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/Transformer.java
index 0bee0218..77156d8a 100644
--- a/commons/src/main/java/io/aiven/kafka/connect/common/source/input/Transformer.java
+++ b/commons/src/main/java/io/aiven/kafka/connect/common/source/input/Transformer.java
@@ -76,7 +76,7 @@ protected abstract static class StreamSpliterator implements Spliterator<SchemaA
          */
         protected final Logger logger;
         /**
-         * The input stream. Will be null until {@link #inputOpened} has completed. May be used for reading but should
+         * * The input stream. Will be null until {@link #inputOpened} has completed. May be used for reading but should
          * not be closed or otherwise made unreadable.
          */
         protected InputStream inputStream;
@@ -131,15 +131,16 @@ public final void close() {
          * Allows modification of input stream. Called immediatly after the input stream is opened. Implementations may
          * modify the type of input stream by wrapping it with a specific implementation, or may create Readers from the
          * input stream. The modified input stream must be returned. If a Reader or similar class is created from the
-         * input stream the input stream must be returned.
+         * input stream the input stream must be returned. The input stream will be null until {@link #inputOpened} has
+         * completed. The implementation of the interface is responsible for closing any newly constructed readers or
+         * input streams in the doClose() method.
          *
          * @param input
          *            the input stream that was just opened.
-         * @return the input stream or modified input stream.
          * @throws IOException
          *             on IO error.
          */
-        abstract protected InputStream inputOpened(InputStream input) throws IOException;
+        abstract protected void inputOpened(InputStream input) throws IOException;
 
         @Override
         public final boolean tryAdvance(final Consumer<? super SchemaAndValue> action) {
diff --git a/commons/src/test/java/io/aiven/kafka/connect/common/config/TransformerFragmentTest.java b/commons/src/test/java/io/aiven/kafka/connect/common/config/TransformerFragmentTest.java
index 1daeb3c8..cb6df54f 100644
--- a/commons/src/test/java/io/aiven/kafka/connect/common/config/TransformerFragmentTest.java
+++ b/commons/src/test/java/io/aiven/kafka/connect/common/config/TransformerFragmentTest.java
@@ -27,6 +27,8 @@
 import org.apache.kafka.common.config.ConfigException;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 class TransformerFragmentTest {
 
@@ -41,21 +43,22 @@ void validateCorrectBufferSizeIsAccepted() {
         assertThat(schemaReg.getTransformerMaxBufferSize()).isEqualTo(bufferSize);
     }
 
-    @Test
-    void validateInvalidBufferSizeThrowsConfigException() {
+    @ParameterizedTest
+    @CsvSource({
+            "21474836471,Invalid value 21474836471 for configuration transformer.max.buffer.size: Not a number of type INT",
+            "-1,transformer.max.buffer.size must be larger then 0 and less then 2147483647",
+            "MAX,Invalid value MAX for configuration transformer.max.buffer.size: Not a number of type INT",
+            "0,transformer.max.buffer.size must be larger then 0 and less then 2147483647",
+            "-9000,transformer.max.buffer.size must be larger then 0 and less then 2147483647",
+            "MTA=,Invalid value MTA= for configuration transformer.max.buffer.size: Not a number of type INT" })
+    void validateInvalidBufferSizeThrowsConfigException(final String value, final String expectedMessage) {
         final ConfigDef configDef = TransformerFragment.update(new ConfigDef());
         final Map<String, Object> props = new HashMap<>();
-        // Too small
-        props.put(TransformerFragment.TRANSFORMER_MAX_BUFFER_SIZE, 0);
 
-        assertThatThrownBy(() -> new TransformerFragment(new AbstractConfig(configDef, props)))
-                .isInstanceOf(ConfigException.class);
-        // Too large
-        props.put(TransformerFragment.TRANSFORMER_MAX_BUFFER_SIZE, Integer.MAX_VALUE + "1");
+        props.put(TransformerFragment.TRANSFORMER_MAX_BUFFER_SIZE, value);
         assertThatThrownBy(() -> new TransformerFragment(new AbstractConfig(configDef, props)))
                 .isInstanceOf(ConfigException.class)
-                .hasMessage(
-                        "Invalid value 21474836471 for configuration transformer.max.buffer.size: Not a number of type INT");
+                .hasMessage(expectedMessage);
     }
 
 }