Insert link in the private message: Input of only spaces in "Text to display" field isn't considered as empty value

Pre-conditions:

#User is logged in

Steps to reproduce:

#Click on the username in the upper right corner of the forum and choose the point "Messages";

#Press the button "Compose";

#Input the valid values into field "To" (for ex. "Антонина Малашок1"), input valid "Subject" (for ex. Test)

#Press "Insert link" button (Ctrl+K);

#In opened form ("Please enter fields values to set URL:") input 5 spaces into the empty field "Text to display";

#Input the valid link into the field "Specify a link" (for ex. http://qa.jtalks.org/jcommune/);

#Press OK button.

#Press Send or Preview button.

AR: the set of spaces is inputed automatically in "Message content" field as Text to display, but we can't preview or send the message, because spaces are considered as empty value for Preview/Send.

ER: the set of spaces in the empty "Text to display" field is considered as empty value for the "Insert link" form, so as a result there will be the text of URL link in the Message content and we haven't any problems to send/preview such message.