Make sure that LogicLib.nsh is included in the nsis include so that the parent script doesn't necessarily need to include it. Quote some things so that they never break when expanded

bin/i2p-zero.nsi

@@ -2,7 +2,9 @@
 !define ZERONAME "I2P-Zero"
 !define I2P64INSTDIR "$PROGRAMFILES64\I2P\"
 !define I2P32INSTDIR "$PROGRAMFILES32\I2P\"
-!define ZEROINSTDIR "$PROGRAMFILES64\${APPNAME}\"
+!define ZEROINSTDIR "$PROGRAMFILES64\${ZERONAME}\"
+# Include the logic library for checking file exists.
+!include LogicLib.nsh
 
 function buildZero
 	!system "echo '#! /usr/bin/env sh' > build-docker.sh"
@@ -24,15 +26,15 @@ function buildZero
 functionEnd
 
 function installZero
-	${If} ${FileExists} `$I2P64INSTDIR\I2P.exe`
-		SetOutPath $ZEROINSTDIR
-	${If} ${FileExists} `$I2P32INSTDIR\I2P.exe`
-		SetOutPath $ZEROINSTDIR
+	${If} ${FileExists} "${I2P64INSTDIR}\I2P.exe"
+		SetOutPath "${ZEROINSTDIR}"
+	${If} ${FileExists} "${I2P32INSTDIR}\I2P.exe"
+		SetOutPath "${ZEROINSTDIR}"
 	${Else}
-		SetOutPath $ZEROINSTDIR
+		SetOutPath "${ZEROINSTDIR}"
 		File /a /r "./I2P-Zero/"
 
-		CreateShortcut "$SMPROGRAMS\Run I2P-Zero.lnk" "$ZEROINSTDIR\router\i2p-zero.exe"
+		CreateShortcut "$SMPROGRAMS\Run I2P-Zero.lnk" "${ZEROINSTDIR}\router\i2p-zero.exe"
 	${EndIf}
 
 functionEnd