diff --git a/mailnews/compose/src/nsMsgSend.cpp b/mailnews/compose/src/nsMsgSend.cpp
index f03155c5b012..6d14d0566908 100644
--- a/mailnews/compose/src/nsMsgSend.cpp
+++ b/mailnews/compose/src/nsMsgSend.cpp
@@ -1133,7 +1133,10 @@ nsMsgComposeAndSend::PreProcessPart(nsMsgAttachmentHandler  *ma,
 
   nsXPIDLCString turl;
   if (!ma->mURL)
-    turl.Adopt(nsCRT::strdup(ma->m_uri));
+    {
+      if (ma->m_uri)
+        turl.Adopt(nsCRT::strdup(ma->m_uri));
+    }
   else
     ma->mURL->GetSpec(getter_Copies(turl));
   hdrs = mime_generate_attachment_headers (ma->m_type, ma->m_encoding,
diff --git a/mailnews/db/msgdb/src/nsMsgOfflineImapOperation.cpp b/mailnews/db/msgdb/src/nsMsgOfflineImapOperation.cpp
index 1eaa1a0ca624..087087688841 100644
--- a/mailnews/db/msgdb/src/nsMsgOfflineImapOperation.cpp
+++ b/mailnews/db/msgdb/src/nsMsgOfflineImapOperation.cpp
@@ -152,7 +152,7 @@ NS_IMETHODIMP nsMsgOfflineImapOperation::GetDestinationFolderURI(char * *aDestin
 
 NS_IMETHODIMP nsMsgOfflineImapOperation::SetDestinationFolderURI(const char * aDestinationFolderURI)
 {
-  m_moveDestination.Adopt(nsCRT::strdup(aDestinationFolderURI));
+  m_moveDestination.Adopt(aDestinationFolderURI ? nsCRT::strdup(aDestinationFolderURI) : 0);
   return m_mdb->SetProperty(m_mdbRow, PROP_MOVE_DEST_FOLDER_URI, aDestinationFolderURI);
 }
 
@@ -167,7 +167,7 @@ NS_IMETHODIMP nsMsgOfflineImapOperation::GetSourceFolderURI(char * *aSourceFolde
 
 NS_IMETHODIMP nsMsgOfflineImapOperation::SetSourceFolderURI(const char * aSourceFolderURI)
 {
-  m_sourceFolder.Adopt(nsCRT::strdup(aSourceFolderURI));
+  m_sourceFolder.Adopt(aSourceFolderURI ? nsCRT::strdup(aSourceFolderURI) : 0);
   SetOperation(kMoveResult);
 
   return m_mdb->SetProperty(m_mdbRow, PROP_SRC_FOLDER_URI, aSourceFolderURI);
diff --git a/mailnews/imap/src/nsImapMailFolder.cpp b/mailnews/imap/src/nsImapMailFolder.cpp
index bcfa5159b40b..b7ece708abf5 100644
--- a/mailnews/imap/src/nsImapMailFolder.cpp
+++ b/mailnews/imap/src/nsImapMailFolder.cpp
@@ -4742,7 +4742,8 @@ nsresult nsImapMailFolder::CopyMessagesOffline(nsIMsgFolder* srcFolder,
         nsXPIDLCString sourceFolderURI;
         srcFolder->GetURI(getter_Copies(sourceFolderURI));
         nsXPIDLCString originalSrcFolderURI;
-        originalSrcFolderURI.Adopt(nsCRT::strdup(sourceFolderURI.get()));
+        if (sourceFolderURI.get())
+          originalSrcFolderURI.Adopt(nsCRT::strdup(sourceFolderURI.get()));
         nsCOMPtr<nsISupports> msgSupports;
         nsCOMPtr<nsIMsgDBHdr> message;
         
@@ -4782,7 +4783,7 @@ nsresult nsImapMailFolder::CopyMessagesOffline(nsIMsgFolder* srcFolder,
               srcFolder->GetURI(getter_Copies(srcFolderURI));
               sourceOp->GetSourceFolderURI(getter_Copies(originalString));
               sourceOp->GetMessageKey(&originalKey);
-              originalSrcFolderURI.Adopt(nsCRT::strdup(originalString.get()));
+              originalSrcFolderURI.Adopt(originalString.get() ? nsCRT::strdup(originalString.get()) : 0);
               
               if (isMove)
                 sourceMailDB->RemoveOfflineOp(sourceOp);
diff --git a/mailnews/local/src/nsMailboxUrl.cpp b/mailnews/local/src/nsMailboxUrl.cpp
index 3e6b68cf726c..f293acf1c177 100644
--- a/mailnews/local/src/nsMailboxUrl.cpp
+++ b/mailnews/local/src/nsMailboxUrl.cpp
@@ -304,7 +304,7 @@ nsMailboxUrl::GetOriginalSpec(char **aSpec)
 NS_IMETHODIMP
 nsMailboxUrl::SetOriginalSpec(const char *aSpec)
 {
-    m_originalSpec.Adopt(nsCRT::strdup(aSpec));
+    m_originalSpec.Adopt(aSpec ? nsCRT::strdup(aSpec) : 0);
     return NS_OK;
 }
 
diff --git a/netwerk/protocol/http/src/nsHttpHandler.cpp b/netwerk/protocol/http/src/nsHttpHandler.cpp
index ad0e84f61665..7ab468ee739c 100644
--- a/netwerk/protocol/http/src/nsHttpHandler.cpp
+++ b/netwerk/protocol/http/src/nsHttpHandler.cpp
@@ -1597,7 +1597,7 @@ nsHttpHandler::GetVendor(char **aVendor)
 NS_IMETHODIMP
 nsHttpHandler::SetVendor(const char *aVendor)
 {
-    mVendor.Adopt(nsCRT::strdup(aVendor));
+    mVendor.Adopt(aVendor ? nsCRT::strdup(aVendor) : 0);
     mUserAgentIsDirty = PR_TRUE;
     return NS_OK;
 }
@@ -1610,7 +1610,7 @@ nsHttpHandler::GetVendorSub(char **aVendorSub)
 NS_IMETHODIMP
 nsHttpHandler::SetVendorSub(const char *aVendorSub)
 {
-    mVendorSub.Adopt(nsCRT::strdup(aVendorSub));
+    mVendorSub.Adopt(aVendorSub ? nsCRT::strdup(aVendorSub) : 0);
     mUserAgentIsDirty = PR_TRUE;
     return NS_OK;
 }
@@ -1623,7 +1623,7 @@ nsHttpHandler::GetVendorComment(char **aVendorComment)
 NS_IMETHODIMP
 nsHttpHandler::SetVendorComment(const char *aVendorComment)
 {
-    mVendorComment.Adopt(nsCRT::strdup(aVendorComment));
+    mVendorComment.Adopt(aVendorComment ? nsCRT::strdup(aVendorComment) : 0);
     mUserAgentIsDirty = PR_TRUE;
     return NS_OK;
 }
@@ -1636,7 +1636,7 @@ nsHttpHandler::GetProduct(char **aProduct)
 NS_IMETHODIMP
 nsHttpHandler::SetProduct(const char *aProduct)
 {
-    mProduct.Adopt(nsCRT::strdup(aProduct));
+    mProduct.Adopt(aProduct ? nsCRT::strdup(aProduct) : 0);
     mUserAgentIsDirty = PR_TRUE;
     return NS_OK;
 }
@@ -1649,7 +1649,7 @@ nsHttpHandler::GetProductSub(char **aProductSub)
 NS_IMETHODIMP
 nsHttpHandler::SetProductSub(const char *aProductSub)
 {
-    mProductSub.Adopt(nsCRT::strdup(aProductSub));
+    mProductSub.Adopt(aProductSub ? nsCRT::strdup(aProductSub) : 0);
     mUserAgentIsDirty = PR_TRUE;
     return NS_OK;
 }
@@ -1662,7 +1662,7 @@ nsHttpHandler::GetProductComment(char **aProductComment)
 NS_IMETHODIMP
 nsHttpHandler::SetProductComment(const char *aProductComment)
 {
-    mProductComment.Adopt(nsCRT::strdup(aProductComment));
+    mProductComment.Adopt(aProductComment ? nsCRT::strdup(aProductComment) : 0);
     mUserAgentIsDirty = PR_TRUE;
     return NS_OK;
 }
@@ -1687,7 +1687,7 @@ nsHttpHandler::GetLanguage(char **aLanguage)
 NS_IMETHODIMP
 nsHttpHandler::SetLanguage(const char *aLanguage)
 {
-    mLanguage.Adopt(nsCRT::strdup(aLanguage));
+    mLanguage.Adopt(aLanguage ? nsCRT::strdup(aLanguage) : 0);
     mUserAgentIsDirty = PR_TRUE;
     return NS_OK;
 }
@@ -1700,7 +1700,7 @@ nsHttpHandler::GetMisc(char **aMisc)
 NS_IMETHODIMP
 nsHttpHandler::SetMisc(const char *aMisc)
 {
-    mMisc.Adopt(nsCRT::strdup(aMisc));
+    mMisc.Adopt(aMisc ? nsCRT::strdup(aMisc) : 0);
     mUserAgentIsDirty = PR_TRUE;
     return NS_OK;
 }
diff --git a/netwerk/protocol/http/src/nsHttpRequestHead.h b/netwerk/protocol/http/src/nsHttpRequestHead.h
index 81f7d3cceaa9..ac9331d15284 100644
--- a/netwerk/protocol/http/src/nsHttpRequestHead.h
+++ b/netwerk/protocol/http/src/nsHttpRequestHead.h
@@ -41,7 +41,7 @@ public:
 
     void SetMethod(nsHttpAtom method) { mMethod = method; }
     void SetVersion(nsHttpVersion version) { mVersion = version; }
-    void SetRequestURI(const char *s) { mRequestURI.Adopt(nsCRT::strdup(s)); }
+    void SetRequestURI(const char *s) { mRequestURI.Adopt(s ? nsCRT::strdup(s) : 0); }
 
     nsHttpHeaderArray &Headers()    { return mHeaders; }
     nsHttpAtom         Method()     { return mMethod; }
diff --git a/netwerk/protocol/http/src/nsHttpResponseHead.h b/netwerk/protocol/http/src/nsHttpResponseHead.h
index 458efcb96222..e898272a1ccc 100644
--- a/netwerk/protocol/http/src/nsHttpResponseHead.h
+++ b/netwerk/protocol/http/src/nsHttpResponseHead.h
@@ -54,7 +54,7 @@ public:
     nsresult GetHeader(nsHttpAtom h, char **v)      { return mHeaders.GetHeader(h, v); }
     void     ClearHeaders()                         { mHeaders.Clear(); }
 
-    void     SetContentType(const char *s) { mContentType.Adopt(nsCRT::strdup(s)); }
+    void     SetContentType(const char *s) { mContentType.Adopt(s ? nsCRT::strdup(s) : 0); }
     void     SetContentLength(PRInt32 len) { mContentLength = len; }
 
     // write out the response status line and headers as a single text block,
diff --git a/rdf/base/src/nsRDFService.cpp b/rdf/base/src/nsRDFService.cpp
index 99913d6ee11e..e932e5f1ec5a 100644
--- a/rdf/base/src/nsRDFService.cpp
+++ b/rdf/base/src/nsRDFService.cpp
@@ -304,7 +304,8 @@ LiteralImpl::GetValue(PRUnichar* *value)
     if (! value)
         return NS_ERROR_NULL_POINTER;
 
-    *value = nsCRT::strdup(GetValue());
+    const PRUnichar *temp = GetValue();
+    *value = temp? nsCRT::strdup(temp) : 0;
     return NS_OK;
 }
 
@@ -1288,7 +1289,7 @@ RDFServiceImpl::RegisterLiteral(nsIRDFLiteral* aLiteral, PRBool aReplace)
 #ifdef REUSE_LITERAL_VALUE_AS_KEY
         PL_HashTableAdd(mLiterals, value, aLiteral);
 #else
-        const PRUnichar* key = nsCRT::strdup(value.get());
+        const PRUnichar* key = value.get() ? nsCRT::strdup(value.get()) : 0;
         if (! key)
             return NS_ERROR_OUT_OF_MEMORY;
 
diff --git a/xpfe/components/directory/nsDirectoryViewer.cpp b/xpfe/components/directory/nsDirectoryViewer.cpp
index b27869ab6065..7e5fcb9b30e5 100644
--- a/xpfe/components/directory/nsDirectoryViewer.cpp
+++ b/xpfe/components/directory/nsDirectoryViewer.cpp
@@ -1295,7 +1295,7 @@ void nsHTTPIndex::GetDestination(nsIRDFResource* r, nsXPIDLCString& dest) {
   if (!url) {
      const char* temp;
      r->GetValueConst(&temp);
-     dest.Adopt(nsCRT::strdup(temp));
+     dest.Adopt(temp ? nsCRT::strdup(temp) : 0);
   } else {
     const PRUnichar* uri;
     url->GetValueConst(&uri);