[MCL-12960] Launcher stucks on Preparing

The launcher works correctly but when i try to download version 1.15.1 it gets stuck on "Preparing" . I've searched over the internet and found so many people have issues related to this but couldn't find any helpful solution.
Console Logs :
[12:42:47 INFO]: Launcher 3.8.0 started on windows...[12:42:47 INFO]: Launcher 3.8.0 started on windows...[12:42:48 INFO]: Current time is Jan 4, 2020 12:42:48 PM[12:42:48 INFO]: System.getProperty('os.name') == 'Windows 8.1'[12:42:48 INFO]: System.getProperty('os.version') == '6.3'[12:42:48 INFO]: System.getProperty('os.arch') == 'amd64'[12:42:48 INFO]: System.getProperty('java.version') == '1.8.0_121'[12:42:48 INFO]: System.getProperty('java.vendor') == 'Oracle Corporation'[12:42:48 INFO]: System.getProperty('sun.arch.data.model') == '64'[12:42:52 INFO]: JFX is already initialized[12:42:57 INFO]: Refreshing local version list...[12:42:58 INFO]: News is up to date![12:42:59 SEVERE]: Couldn't load local version C:\Users\sara m m\AppData\Roaming\.minecraft\versions\1.15.1\1.15.1.jsoncom.google.gson.JsonSyntaxException: duplicate key: null at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:191) at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:146) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) at com.google.gson.Gson.fromJson(Gson.java:795) at com.google.gson.Gson.fromJson(Gson.java:761) at com.google.gson.Gson.fromJson(Gson.java:710) at com.google.gson.Gson.fromJson(Gson.java:682) at net.minecraft.launcher.updater.LocalVersionList.refreshVersions(Unknown Source) at net.minecraft.launcher.updater.a.refreshVersions(Unknown Source) at net.minecraft.launcher.Launcher$3.run(Unknown Source) at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.util.concurrent.FutureTask.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source)
[12:42:59 SEVERE]: Couldn't load local version C:\Users\sara m m\AppData\Roaming\.minecraft\versions\1.15.1-forge-30.0.17\1.15.1-forge-30.0.17.jsoncom.google.gson.JsonSyntaxException: java.net.MalformedURLException: no protocol:  at com.google.gson.Gson.fromJson(Gson.java:809) at com.google.gson.Gson.fromJson(Gson.java:761) at com.google.gson.Gson.fromJson(Gson.java:710) at com.google.gson.Gson.fromJson(Gson.java:682) at net.minecraft.launcher.updater.LocalVersionList.refreshVersions(Unknown Source) at net.minecraft.launcher.updater.a.refreshVersions(Unknown Source) at net.minecraft.launcher.Launcher$3.run(Unknown Source) at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.util.concurrent.FutureTask.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source)Caused by: java.net.MalformedURLException: no protocol:  at java.net.URL.<init>(Unknown Source) at java.net.URL.<init>(Unknown Source) at java.net.URL.<init>(Unknown Source) at com.google.gson.internal.bind.TypeAdapters$18.read(TypeAdapters.java:439) at com.google.gson.internal.bind.TypeAdapters$18.read(TypeAdapters.java:431) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:81) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:60) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) at com.google.gson.Gson.fromJson(Gson.java:795) ... 11 more
[12:42:59 INFO]: Refreshing remote version list...[12:43:05 INFO]: Refresh complete.[12:43:08 INFO]: Installed CompleteVersion{id='1.12.2', updatedTime=Mon Sep 18 01:39:46 PDT 2017, releasedTime=Mon Sep 18 01:39:46 PDT 2017, type=RELEASE, libraries=[Library{name='com.mojang:patchy:1.1', rules=null, natives=null, extract=null}, Library{name='oshi-project:oshi-core:1.1', rules=null, natives=null, extract=null}, Library{name='net.java.dev.jna:jna:4.4.0', rules=null, natives=null, extract=null}, Library{name='net.java.dev.jna:platform:3.4.0', rules=null, natives=null, extract=null}, Library{name='com.ibm.icu:icu4j-core-mojang:51.2', rules=null, natives=null, extract=null}, Library{name='net.sf.jopt-simple:jopt-simple:5.0.3', rules=null, natives=null, extract=null}, Library{name='com.paulscode:codecjorbis:20101023', rules=null, natives=null, extract=null}, Library{name='com.paulscode:codecwav:20101023', rules=null, natives=null, extract=null}, Library{name='com.paulscode:libraryjavasound:20101123', rules=null, natives=null, extract=null}, Library{name='com.paulscode:librarylwjglopenal:20100824', rules=null, natives=null, extract=null}, Library{name='com.paulscode:soundsystem:20120107', rules=null, natives=null, extract=null}, Library{name='io.netty:netty-all:4.1.9.Final', rules=null, natives=null, extract=null}, Library{name='com.google.guava:guava:21.0', rules=null, natives=null, extract=null}, Library{name='org.apache.commons:commons-lang3:3.5', rules=null, natives=null, extract=null}, Library{name='commons-io:commons-io:2.5', rules=null, natives=null, extract=null}, Library{name='commons-codec:commons-codec:1.10', rules=null, natives=null, extract=null}, Library{name='net.java.jinput:jinput:2.0.5', rules=null, natives=null, extract=null}, Library{name='net.java.jutils:jutils:1.0.0', rules=null, natives=null, extract=null}, Library{name='com.google.code.gson:gson:2.8.0', rules=null, natives=null, extract=null}, Library{name='com.mojang:authlib:1.5.25', rules=null, natives=null, extract=null}, Library{name='com.mojang:realms:1.10.22', rules=null, natives=null, extract=null}, Library{name='org.apache.commons:commons-compress:1.8.1', rules=null, natives=null, extract=null}, Library{name='org.apache.httpcomponents:httpclient:4.3.3', rules=null, natives=null, extract=null}, Library{name='commons-logging:commons-logging:1.1.3', rules=null, natives=null, extract=null}, Library{name='org.apache.httpcomponents:httpcore:4.3.2', rules=null, natives=null, extract=null}, Library{name='it.unimi.dsi:fastutil:7.1.0', rules=null, natives=null, extract=null}, Library{name='org.apache.logging.log4j:log4j-api:2.8.1', rules=null, natives=null, extract=null}, Library{name='org.apache.logging.log4j:log4j-core:2.8.1', rules=null, natives=null, extract=null}, Library{name='org.lwjgl.lwjgl:lwjgl:2.9.4-nightly-20150209', rules=[Rule{action=ALLOW, os=null, features=null}, Rule{action=DISALLOW, os=OSRestriction{name=OSX, version='null', arch='null'}, features=null}], natives=null, extract=null}, Library{name='org.lwjgl.lwjgl:lwjgl_util:2.9.4-nightly-20150209', rules=[Rule{action=ALLOW, os=null, features=null}, Rule{action=DISALLOW, os=OSRestriction{name=OSX, version='null', arch='null'}, features=null}], natives=null, extract=null}, Library{name='org.lwjgl.lwjgl:lwjgl-platform:2.9.4-nightly-20150209', rules=[Rule{action=ALLOW, os=null, features=null}, Rule{action=DISALLOW, os=OSRestriction{name=OSX, version='null', arch='null'}, features=null}], natives={LINUX=natives-linux, OSX=natives-osx, WINDOWS=natives-windows}, extract=com.mojang.launcher.versions.ExtractRules@3371bedc}, Library{name='org.lwjgl.lwjgl:lwjgl:2.9.2-nightly-20140822', rules=[Rule{action=ALLOW, os=OSRestriction{name=OSX, version='null', arch='null'}, features=null}], natives=null, extract=null}, Library{name='org.lwjgl.lwjgl:lwjgl_util:2.9.2-nightly-20140822', rules=[Rule{action=ALLOW, os=OSRestriction{name=OSX, version='null', arch='null'}, features=null}], natives=null, extract=null}, Library{name='org.lwjgl.lwjgl:lwjgl-platform:2.9.2-nightly-20140822', rules=[Rule{action=ALLOW, os=OSRestriction{name=OSX, version='null', arch='null'}, features=null}], natives={LINUX=natives-linux, OSX=natives-osx, WINDOWS=natives-windows}, extract=com.mojang.launcher.versions.ExtractRules@2427438d}, Library{name='net.java.jinput:jinput-platform:2.0.5', rules=null, natives={LINUX=natives-linux, OSX=natives-osx, WINDOWS=natives-windows}, extract=com.mojang.launcher.versions.ExtractRules@5cdc31da}, Library{name='com.mojang:text2speech:1.10.3', rules=null, natives=null, extract=null}, Library{name='com.mojang:text2speech:1.10.3', rules=null, natives={LINUX=natives-linux, WINDOWS=natives-windows}, extract=com.mojang.launcher.versions.ExtractRules@4db66b6b}, Library{name='ca.weblite:java-objc-bridge:1.0.0', rules=[Rule{action=ALLOW, os=OSRestriction{name=OSX, version='null', arch='null'}, features=null}], natives={OSX=natives-osx}, extract=com.mojang.launcher.versions.ExtractRules@730fab5f}, Library{name='ca.weblite:java-objc-bridge:1.0.0', rules=[Rule{action=ALLOW, os=OSRestriction{name=OSX, version='null', arch='null'}, features=null}], natives=null, extract=null}], mainClass='net.minecraft.client.main.Main', jar='null', minimumLauncherVersion=18}[12:43:10 INFO]: Loaded 5 profile(s); selected 'forge'[12:43:23 INFO]: Getting syncinfo for selected version[12:43:23 INFO]: Queueing library & version downloads[12:43:24 SEVERE]: Unhandled exception in thread Thread[pool-1-thread-2,5,main]com.google.gson.JsonSyntaxException: duplicate key: null at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:191) at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:146) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172) at com.google.gson.Gson.fromJson(Gson.java:795) at com.google.gson.Gson.fromJson(Gson.java:761) at com.google.gson.Gson.fromJson(Gson.java:710) at com.google.gson.Gson.fromJson(Gson.java:682) at net.minecraft.launcher.updater.RemoteVersionList.getCompleteVersion(Unknown Source) at net.minecraft.launcher.updater.a.b(Unknown Source) at net.minecraft.launcher.updater.a.getLatestCompleteVersion(Unknown Source) at com.mojang.launcher.game.runner.AbstractGameRunner.playGame(Unknown Source) at net.minecraft.launcher.game.GameLaunchDispatcher$1.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source)
Thanks