Segmentation fault on prepare_cached with an empty query

With an empty query is prepared, sqlite3 returns no error but a null pointer.
And then `sqlite3_sql` returns null.
Which make `CStr::from_ptr` crash.

src/cache.rs

@@ -135,9 +135,12 @@ impl StatementCache {
 
     // Return a statement to the cache.
     fn cache_stmt(&self, stmt: RawStatement) {
+        if stmt.is_null() {
+            return;
+        }
         let mut cache = self.0.borrow_mut();
         stmt.clear_bindings();
-        let sql = String::from_utf8_lossy(stmt.sql().to_bytes())
+        let sql = String::from_utf8_lossy(stmt.sql().unwrap().to_bytes())
             .trim()
             .to_string();
         cache.insert(sql, stmt);
@@ -339,4 +342,10 @@ mod test {
         }
         assert_eq!(1, cache.len());
     }
+
+    #[test]
+    fn test_empty_stmt() {
+        let conn = Connection::open_in_memory().unwrap();
+        conn.prepare_cached("").unwrap();
+    }
 }

src/inner_connection.rs

@@ -90,9 +90,17 @@ impl InnerConnection {
                 } else {
                     let mut e = error_from_handle(db, r);
                     if let Error::SqliteFailure(
-                        ffi::Error{code: ffi::ErrorCode::CannotOpen, extended_code: _}, Some(msg)) = e {
+                        ffi::Error {
+                            code: ffi::ErrorCode::CannotOpen,
+                            extended_code: _,
+                        },
+                        Some(msg),
+                    ) = e
+                    {
                         e = Error::SqliteFailure(
-                            ffi::Error::new(r), Some(format!("{}: {}", msg, c_path.to_string_lossy())));
+                            ffi::Error::new(r),
+                            Some(format!("{}: {}", msg, c_path.to_string_lossy())),
+                        );
                     }
                     ffi::sqlite3_close(db);
                     e

src/lib.rs

@@ -966,7 +966,12 @@ mod test {
         if let Error::SqliteFailure(e, Some(msg)) = err {
             assert_eq!(ErrorCode::CannotOpen, e.code);
             assert_eq!(ffi::SQLITE_CANTOPEN, e.extended_code);
-            assert!(msg.contains(filename), "error message '{}' does not contain '{}'", msg, filename);
+            assert!(
+                msg.contains(filename),
+                "error message '{}' does not contain '{}'",
+                msg,
+                filename
+            );
         } else {
             panic!("SqliteFailure expected");
         }

src/raw_statement.rs

@@ -14,6 +14,10 @@ impl RawStatement {
         RawStatement(stmt, tail)
     }
 
+    pub fn is_null(&self) -> bool {
+        self.0.is_null()
+    }
+
     pub unsafe fn ptr(&self) -> *mut ffi::sqlite3_stmt {
         self.0
     }
@@ -95,8 +99,12 @@ impl RawStatement {
         unsafe { ffi::sqlite3_clear_bindings(self.0) }
     }
 
-    pub fn sql(&self) -> &CStr {
-        unsafe { CStr::from_ptr(ffi::sqlite3_sql(self.0)) }
+    pub fn sql(&self) -> Option<&CStr> {
+        if self.0.is_null() {
+            None
+        } else {
+            Some(unsafe { CStr::from_ptr(ffi::sqlite3_sql(self.0)) })
+        }
     }
 
     pub fn finalize(mut self) -> c_int {

src/statement.rs

@@ -625,7 +625,11 @@ impl Into<RawStatement> for Statement<'_> {
 
 impl fmt::Debug for Statement<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let sql = str::from_utf8(self.stmt.sql().to_bytes());
+        let sql = if self.stmt.is_null() {
+            Ok("")
+        } else {
+            str::from_utf8(self.stmt.sql().unwrap().to_bytes())
+        };
         f.debug_struct("Statement")
             .field("conn", self.conn)
             .field("stmt", &self.stmt)