Fix potential "caretPosition is null" bug

src/directives/compose_area.ts

@@ -87,7 +87,8 @@ export default [
                     from?: number,
                     to?: number,
                     fromBytes?: number,
-                    toBytes?: number } = null;
+                    toBytes?: number,
+                } = null;
 
                 /**
                  * Stop propagation of click events and hold htmlElement of the emojipicker
@@ -293,7 +294,7 @@ export default [
                         const text = getText(false);
                         if (text === '\n') {
                             composeDiv[0].innerText = '';
-                        } else if (ev.keyCode === 190) {
+                        } else if (ev.keyCode === 190 && caretPosition !== null) {
                             // A ':' is pressed, try to parse
                             const currentWord = stringService.getWord(text, caretPosition.fromBytes, [':']);
                             if (currentWord.realLength > 2
@@ -308,7 +309,7 @@ export default [
                         }
 
                         // Update typing information (use text instead method)
-                        if (text.trim().length === 0) {
+                        if (text.trim().length === 0 || caretPosition === null) {
                             stopTyping();
                             scope.onTyping('');
                         } else {