diff --git a/cliutils.nim b/cliutils.nim
index 55d385e..1f9cfa0 100644
--- a/cliutils.nim
+++ b/cliutils.nim
@@ -41,20 +41,20 @@ type HandleProcMsgCB* = proc (outMsg: TaintedString,
                               errMsg: TaintedString, cmd: string): void
 
 proc sendMsg*(h: HandleProcMsgCB, outMsg: TaintedString,
-              errMsg: TaintedString = nil, cmd: string = ""): void =
+              errMsg: TaintedString = "", cmd: string = ""): void =
   if h != nil: h(outMsg, errMsg, cmd)
 
 proc makeProcMsgHandler*(outSink, errSink: File, prefixCmd: bool = true): HandleProcMsgCB =
   result = proc(outMsg, errMsg: TaintedString, cmd: string): void {.closure.} =
-    let prefix = if cmd == nil or not prefixCmd: "" else: cmd & ": "
-    if outMsg != nil: outSink.writeLine(prefix & outMsg)
-    if errMsg != nil: errSink.writeLine(prefix & errMsg)
+    let prefix = if cmd.len == 0 or not prefixCmd: "" else: cmd & ": "
+    if outMsg.len > 0: outSink.writeLine(prefix & outMsg)
+    if errMsg.len > 0: errSink.writeLine(prefix & errMsg)
 
 proc makeProcMsgHandler*(outSink, errSink: Stream, prefixCmd: bool = true): HandleProcMsgCB =
   result = proc(outMsg, errMsg: TaintedString, cmd: string): void {.closure.} =
-    let prefix = if cmd == nil or not prefixCmd: "" else: cmd & ": "
-    if outMsg != nil: outSink.writeLine(prefix & outMsg)
-    if errMsg != nil: errSink.writeLine(prefix & errMsg)
+    let prefix = if cmd.len == 0 or not prefixCmd: "" else: cmd & ": "
+    if outMsg.len > 0: outSink.writeLine(prefix & outMsg)
+    if errMsg.len > 0: errSink.writeLine(prefix & errMsg)
 
 proc combineProcMsgHandlers*(a, b: HandleProcMsgCB): HandleProcMsgCB =
   if a == nil: result = b
@@ -72,9 +72,9 @@ proc waitFor*(p: Process, msgCB: HandleProcMsgCB, procCmd: string = ""): int =
   var line = newStringOfCap(120).TaintedString
   while true:
     if pout.readLine(line):
-      msgCB.sendMsg(line, nil, procCmd)
+      msgCB.sendMsg(line, "", procCmd)
     elif perr.readLine(line):
-      msgCB.sendMsg(nil, line, procCmd)
+      msgCB.sendMsg("", line, procCmd)
     else:
       result = peekExitCode(p)
       if result != -1: break
@@ -100,8 +100,8 @@ proc execWithOutput*(command: string, workingDir:string = "",
   outSeq = @[]; errSeq = @[]
   var outputCollector = combineProcMsgHandlers(msgCB,
     proc(outMsg, errMsg: TaintedString, cmd: string): void {.closure.} =
-      if outMsg != nil: outSeq.add(outMsg)
-      if errMsg != nil: errSeq.add(errMsg))
+      if outMsg.len > 0: outSeq.add(outMsg)
+      if errMsg.len > 0: errSeq.add(errMsg))
 
   result[2] = exec(command, workingDir, args, env, options, outputCollector)
   result[0] = outSeq.join("\n")
@@ -147,15 +147,15 @@ proc daemonize*(pidfile, si, so, se: string, daemonMain: proc(): void): Pid =
     flushFile(stdout)
     flushFile(stderr)
 
-    if not si.isNil and si != "":
+    if si.len > 0:
       fi = open(si, fmRead)
       discard dup2(getFileHandle(fi), getFileHandle(stdin))
 
-    if not so.isNil and so != "":
+    if so.len > 0:
       fo = open(so, fmAppend)
       discard dup2(getFileHandle(fo), getFileHandle(stdout))
 
-    if not se.isNil and so != "":
+    if se.len > 0:
       fe = open(se, fmAppend)
       discard dup2(getFileHandle(fe), getFileHandle(stderr))
 
diff --git a/cliutils.nimble b/cliutils.nimble
index 2bc240f..3eec9f1 100644
--- a/cliutils.nimble
+++ b/cliutils.nimble
@@ -1,11 +1,11 @@
 # Package
 
-version       = "0.5.0"
+version       = "0.6.0"
 author        = "Jonathan Bernard"
 description   = "Helper functions for writing command line interfaces."
 license       = "MIT"
 
 # Dependencies
 
-requires @["nim >= 0.18.0", "docopt"]
+requires @["nim >= 0.19.0", "docopt >= 0.6.8"]