fixed style issues and added test for null supplier

src/main/java/org/apache/commons/cli/CommandLine.java

@@ -438,7 +438,7 @@ public <T> T getParsedOptionValue(final char opt, final Supplier<T> defaultValue
      * @since 1.5.0
      */
     public <T> T getParsedOptionValue(final Option option) throws ParseException {
-        return  getParsedOptionValue(option, ()-> null);
+        return  getParsedOptionValue(option, () -> null);
     }
 
     /**
@@ -472,7 +472,10 @@ public <T> T getParsedOptionValue(final Option option, final Supplier<T> default
         final String res = option == null ? null : getOptionValue(option);
 
         try {
-            return res == null ? defaultValue.get() : (T) option.getConverter().apply(res);
+            if (res == null) {
+                return defaultValue == null ? null : defaultValue.get();
+            }
+            return (T) option.getConverter().apply(res);
         } catch (final Throwable e) {
             throw ParseException.wrap(e);
         }

src/test/java/org/apache/commons/cli/CommandLineTest.java

@@ -22,6 +22,7 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import static org.junit.Assert.assertNull;
 
 import java.util.Properties;
+import java.util.function.Supplier;
 
 import org.junit.Test;
 
@@ -150,6 +151,18 @@ public void testGetParsedOptionValueWithChar() throws Exception {
         assertEquals("foo", cmd.getParsedOptionValue('f'));
     }
 
+    @Test
+    public void testGetParsedOptionValueWithNullSupplier() throws Exception {
+        final Options options = new Options();
+        options.addOption(Option.builder("i").hasArg().type(Number.class).build());
+
+        final CommandLineParser parser = new DefaultParser();
+        final CommandLine cmd = parser.parse(options, new String[0]);
+        final Supplier<Number> supplier = null;
+
+        assertNull(cmd.getParsedOptionValue('i', supplier));
+    }
+
     @Test
     public void testGetParsedOptionValueWithOption() throws Exception {
         final Options options = new Options();
@@ -178,11 +191,11 @@ public void testGetParsedOptionValueUsingDefault() throws Exception {
 
         assertEquals(123, ((Number) cmd.getParsedOptionValue(optI)).intValue());
         assertEquals("foo", cmd.getParsedOptionValue(optF, "foo"));
-        assertEquals("foo", cmd.getParsedOptionValue(optF, ()-> "foo"));
+        assertEquals("foo", cmd.getParsedOptionValue(optF, () -> "foo"));
         assertEquals("foo", cmd.getParsedOptionValue("f", "foo"));
-        assertEquals("foo", cmd.getParsedOptionValue("f", ()-> "foo"));
+        assertEquals("foo", cmd.getParsedOptionValue("f", () -> "foo"));
         assertEquals("foo", cmd.getParsedOptionValue('f', "foo"));
-        assertEquals("foo", cmd.getParsedOptionValue('f', ()-> "foo"));
+        assertEquals("foo", cmd.getParsedOptionValue('f', () -> "foo"));
     }
 
     @Test