Index: src/main/groovy/lang/MetaClassImpl.java
===================================================================
--- src/main/groovy/lang/MetaClassImpl.java	(revision 19149)
+++ src/main/groovy/lang/MetaClassImpl.java	(working copy)
@@ -2864,7 +2864,6 @@
             Object method = iter.next();
             ParameterTypes paramTypes = (ParameterTypes) method;
             long dist = MetaClassHelper.calculateParameterDistance(arguments, paramTypes);
-            if (dist == 0) return method;
             if (matches.size() == 0) {
                 matches.add(method);
                 matchesDistance = dist;
Index: src/test/groovy/bugs/Groovy4029Bug.groovy
===================================================================
--- src/test/groovy/bugs/Groovy4029Bug.groovy	(revision 0)
+++ src/test/groovy/bugs/Groovy4029Bug.groovy	(revision 0)
@@ -0,0 +1,9 @@
+package groovy.bugs
+
+class Groovy4029Bug extends GroovyTestCase {
+    void testAddNullKeyEntryInMapUsingSubscriptNotation() {
+		Map m = [:]
+		m[null] = null
+		assert m.size() == 1
+    }
+}