Prevents null type from being used in tuple.

test/libsolidity/syntaxTests/types/empty_tuple_event.sol

@@ -0,0 +1,10 @@
+pragma solidity ^0.4.3;
+contract C {
+    event SomeEvent();
+    function a() public {
+        (SomeEvent(), 7);
+    }
+}
+// ----
+// Warning: (95-106): Invoking events without "emit" prefix is deprecated.
+// TypeError: (95-106): Type of tuple component cannot be null.

test/libsolidity/syntaxTests/types/empty_tuple_event_050.sol

@@ -0,0 +1,10 @@
+pragma experimental "v0.5.0";
+contract C {
+    event SomeEvent();
+    function a() public {
+        (SomeEvent(), 7);
+    }
+}
+// ----
+// TypeError: (101-112): Event invocations have to be prefixed by "emit".
+// TypeError: (101-112): Type of tuple component cannot be null.

test/libsolidity/syntaxTests/types/empty_tuple_function.sol

@@ -0,0 +1,11 @@
+pragma solidity ^0.4.3;
+contract C {
+    function f() {}
+    function a() public {
+        bool x = true;
+        bool y = true;
+        (x) ? (f(), y = false) : (f(), y = false);
+    }
+}
+// ----
+// TypeError: (144-147): Type of tuple component cannot be null.

test/libsolidity/syntaxTests/types/empty_tuple_function_self.sol

@@ -0,0 +1,8 @@
+pragma solidity ^0.4.3;
+contract C {
+    function a() public {
+        (a(), 7);
+    }
+}
+// ----
+// TypeError: (72-75): Type of tuple component cannot be null.

test/libsolidity/syntaxTests/types/empty_tuple_lvalue.sol

@@ -0,0 +1,11 @@
+pragma solidity ^0.4.3;
+contract C {
+    function f() public pure {}
+    function a() public {
+        uint x;
+        uint y;
+        (x, y) = (f(), f());
+    }
+}
+// ----
+// TypeError: (145-148): Type of tuple component cannot be null.