Inserted data gets a space between

I am using a plugin to authenticate my users , I am modifyig it but somehow it is adding a huge white space between first and last name,,,

I am not sure, as dont know much about php, but is it anything here that might be causing this issue?

// to authenticate, the username must exist in the       if ($credentials['password'] ==  substr ($row->$passwordfield,-4) )
			
        {
            if (!empty($firstnamefield)){
                $fullname = $row->$firstnamefield;
            }
		
            if (!empty($lastnamefield)){
                $fullname .= ' '.$row->$lastnamefield;
            }

	            $response->fullname = $fullname;

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