SERVER-31516 Fix improper initialization of empty NamespaceString.

(cherry picked from commit e7390933e152d8e6f00c90ac341f691780c261fd)

Conflicts:
	src/mongo/db/namespace_string_test.cpp

2 files changed, 14 insertions, 1 deletions

diff --git a/src/mongo/db/namespace_string-inl.h b/src/mongo/db/namespace_string-inl.h
index 8e8808fb9b8..7deeffc5bd4 100644
--- a/src/mongo/db/namespace_string-inl.h
+++ b/src/mongo/db/namespace_string-inl.h
@@ -112,7 +112,7 @@ inline bool NamespaceString::validCollectionName(StringData coll) {
     return true;
 }
 
-inline NamespaceString::NamespaceString() : _ns(), _dotIndex(0) {}
+inline NamespaceString::NamespaceString() : _ns(), _dotIndex(std::string::npos) {}
 inline NamespaceString::NamespaceString(StringData nsIn) {
     _ns = nsIn.toString();  // copy to our buffer
     _dotIndex = _ns.find('.');
diff --git a/src/mongo/db/namespace_string_test.cpp b/src/mongo/db/namespace_string_test.cpp
index ba85cc775e3..2fd35bdd225 100644
--- a/src/mongo/db/namespace_string_test.cpp
+++ b/src/mongo/db/namespace_string_test.cpp
@@ -234,4 +234,17 @@ TEST(NamespaceStringTest, NamespaceStringParse4) {
     ASSERT_EQUALS((string) "abc", ns.db());
     ASSERT_EQUALS((string) "", ns.coll());
 }
+
+
+TEST(NamespaceStringTest, EmptyNSStringReturnsEmptyColl) {
+    NamespaceString nss{};
+    ASSERT_TRUE(nss.toString().empty());
+    ASSERT_EQ(nss.coll(), StringData{});
+}
+
+TEST(NamespaceStringTest, EmptyNSStringReturnsEmptyDb) {
+    NamespaceString nss{};
+    ASSERT_TRUE(nss.toString().empty());
+    ASSERT_EQ(nss.db(), StringData{});
+}
 }