Config: Distinguish between empty and null strings

The C git API and command line tools distinguish between a key having
the empty string as a value and no key being present in the config
file:

$ echo -e '[a]\nx =' > foo.config
$ git config -f foo.config a.x; echo $?

0
$ git config -f foo.config a.y; echo $?
1

Make JGit make the same distinction. This is in line with the current
Javadoc of getString, which claims to return "a String value from the
config, null if not found". It is more reasonable to interpret "x ="
in the above example as "found" rather than "missing".

We need to maintain the special handling of a key name with no "="
resolving to a boolean true, but "=" with an empty string is still not
a valid boolean.

Change-Id: If0dbb7470c524259de0b167148db87f81be2d04a

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ConfigTest.java

@@ -51,7 +51,6 @@ package org.eclipse.jgit.lib;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
@@ -502,27 +501,6 @@ public class ConfigTest {
 		assertEquals("[my]\n\tempty\n", c.toText());
 	}
 
-	@Test
-	public void testEmptyString() throws ConfigInvalidException {
-		Config c = parse("[my]\n\tempty =\n");
-		assertNull(c.getString("my", null, "empty"));
-
-		String[] values = c.getStringList("my", null, "empty");
-		assertNotNull(values);
-		assertEquals(1, values.length);
-		assertNull(values[0]);
-
-		// always matches the default, because its non-boolean
-		assertTrue(c.getBoolean("my", "empty", true));
-		assertFalse(c.getBoolean("my", "empty", false));
-
-		assertEquals("[my]\n\tempty =\n", c.toText());
-
-		c = new Config();
-		c.setStringList("my", null, "empty", Arrays.asList(values));
-		assertEquals("[my]\n\tempty =\n", c.toText());
-	}
-
 	@Test
 	public void testUnsetBranchSection() throws ConfigInvalidException {
 		Config c = parse("" //
@@ -699,6 +677,55 @@ public class ConfigTest {
 		assertEquals("1", c.getString("a", null, "y"));
 	}
 
+	@Test
+	public void testExplicitlySetEmptyString() throws Exception {
+		Config c = new Config();
+		c.setString("a", null, "x", "0");
+		c.setString("a", null, "y", "");
+
+		assertEquals("0", c.getString("a", null, "x"));
+		assertEquals(0, c.getInt("a", null, "x", 1));
+
+		assertEquals("", c.getString("a", null, "y"));
+		assertArrayEquals(new String[]{""}, c.getStringList("a", null, "y"));
+		try {
+			c.getInt("a", null, "y", 1);
+		} catch (IllegalArgumentException e) {
+			assertEquals("Invalid integer value: a.y=", e.getMessage());
+		}
+
+		assertNull(c.getString("a", null, "z"));
+		assertArrayEquals(new String[]{}, c.getStringList("a", null, "z"));
+	}
+
+	@Test
+	public void testParsedEmptyString() throws Exception {
+		Config c = parse("[a]\n"
+				+ "x = 0\n"
+				+ "y =\n");
+
+		assertEquals("0", c.getString("a", null, "x"));
+		assertEquals(0, c.getInt("a", null, "x", 1));
+
+		assertEquals("", c.getString("a", null, "y"));
+		assertArrayEquals(new String[]{""}, c.getStringList("a", null, "y"));
+		try {
+			c.getInt("a", null, "y", 1);
+		} catch (IllegalArgumentException e) {
+			assertEquals("Invalid integer value: a.y=", e.getMessage());
+		}
+
+		assertNull(c.getString("a", null, "z"));
+		assertArrayEquals(new String[]{}, c.getStringList("a", null, "z"));
+	}
+
+	@Test
+	public void testSetStringListWithEmptyValue() throws Exception {
+		Config c = new Config();
+		c.setStringList("a", null, "x", Arrays.asList(""));
+		assertArrayEquals(new String[]{""}, c.getStringList("a", null, "x"));
+	}
+
 	private static void assertReadLong(long exp) throws ConfigInvalidException {
 		assertReadLong(exp, String.valueOf(exp));
 	}

org.eclipse.jgit/src/org/eclipse/jgit/lib/Config.java

@@ -1268,7 +1268,7 @@ public class Config {
 
 			value.append((char) c);
 		}
-		return value.length() > 0 ? value.toString() : null;
+		return value.toString();
 	}
 
 	/**